Transfer Sample App

The Pay My Bills sample app is a demonstration of how a company (in this case, a fictional utility company) can use Plaid Transfer to allow their customers to utilize pay by bank to pay their electric bills.

This demo app shows two different ways to use Plaid Transfer -- one method using Transfer UI (which handles several intermediate steps and collects appropriate proof of authorization), and another method where you have to perform those steps yourself.

This app uses NodeJS on the backend (with Express as the server), SQLite as the database, and plain ol' vanilla JavaScript on the frontend. It designed to be simple enough that a Python engineer without a lot of deep JavaScript experience could still understand what's going on and follow along in a video tutorial, so we avoid too much idiomatic JavaScript. That said, you should be familiar with destructuring and object property shorthand.

Installation

We recommend having node version 18.x.x or later before attempting to run this application.

1. Make sure you have access to Transfer

First, if you haven't already done so, sign up for your free Plaid API keys.

If you have a relatively new Plaid developer account, you should already have access to Transfer in Sandbox. If you don't, please contact support and you can get access to Transfer in the Sandbox environment without needing to apply for the full product.

If you don't have access to Transfer, you can still follow along with this Quickstart by watching the Video Walkthrough (URL to be added later)

2. Clone the repository

Using https:

git clone https://github.com/plaid/transfer-quickstart
cd transfer-quickstart

Alternatively, if you use ssh:

git clone git@github.com:plaid/transfer-quickstart.git
cd transfer-quickstart

3. Install the required packages

Run npm install inside your directory to install the Node packages required for this application to run.

4. Set up your environment variables

Copy .env.template to a new file called .env. Then open up .env in your favorite code editor and fill out the values specified there.

cp .env.template .env

You can get your PLAID_CLIENT_ID and PLAID_SECRET values from the Keys section of the Plaid dashboard

Keep sandbox as your environment.

You can probably keep START_SYNC_NUM as 0, unless your client is part of a team that has already been using Plaid Transfer extensively.

NOTE: .env files are a convenient local development tool. Never run a production application using an environment file with secrets in it. Use some kind of Secrets Manager (provided by most commercial cloud providers) instead.

5. (Optional) Set up your webhook receiver

Transfer makes use of webhooks to let applications know that the status of a payment has changed. If you want to see this part of the application in action, you will need to tell Plaid what webhook receiver it should send these messages to.

Step 1: Create a public endpoint for your webhook receiver

This webhook receiver will need to be available to the public in order for Plaid to communicate with it. If you don't wish to publish your sample application to a public server, one common option is to use a tool like ngrok to open up a tunnel from the outside world to a specific port running on localhost.

The sample application uses a separate server to receive webhooks running on port 8001, so if you have ngrok installed, you can run

ngrok http 8001

to open up a tunnel from the outside world to this server. The final URL will be the domain that ngrok has created, plus the path /server/receive_webhook. It will probably look something like:

https://abde-123-4-567-8.ngrok.io/server/receive_webhook

Step 2: Add this URL to the .env file

Normally, you would use the Webhooks section of the Plaid dashboard to tell Plaid what endpoint to call when a Transfer event happens.

However, when you are running Transfer in the Sandbox environment, Transfer won't regularly send any webhooks. You'll need to tell Plaid, through its /sandbox/transfer/fire_webhook endpoint, to fire a webhook and to what URL. Our sample application grabs the URL to use from the SANDBOX_WEBHOOK_URL value in the .env file.

7. Run the application!

You can run your application by typing

npm run watch

on the command line. If there are no issues, you should see a message telling you that you can open up http://localhost:8000/ to view your running app!

Running the application

Pay Your Electric Bill is a fictional website that utilizes Plaid Transfer so that customers can use pay-by-bank to pay their electric bill.

This sample application simulates two different ways that a user could use Plaid Transfer to pay by bank. Obviously, in a real app, you wouldn't use both options; this is just for demonstration purposes.

Create a fictional customer account or sign in with a existing account to start the process.

To create a bill, simply click the Generate a new bill button. One will be randomly generated for you.

1. Paying your bill with Transfer UI

Transfer UI is a feature built into Link, the UI widget provided by Plaid. It takes care of connecting your user to a checking or savings account if necessary, and then properly collecting proof of authorization data to ensure you stay compliant with Nacha guidelines.

Using Transfer UI doesn't require installing any additional libraries on the client -- it's already part of Link.

To pay your bill using Tranfer UI, click the "Pay" link next to any individual bill. This will take you to a Bill Details page where you can see details about your bill, including the original amount, and how much is still due.

From the Bill Details page, enter an amount to pay and click the Pay Bill button.

If this is your first time using this application and you have not connected Plaid to any checking or savings accounts with this user, Plaid will prompt you to connect to a new bank.

Go through the standard process for connecting to a new bank in Sandbox -- pick any institution you'd like, enter user_good and pass_good as the user name and password, and enter 1234 for an MFA code if prompted.

Once you're done connecting to a bank, Plaid will then ask you to authorize a payment from the account you've just connected to. Click Accept, and your payment is submitted.

To make subsequent payments with the same account, select the account you've previously connected, enter an amount, and click "Pay". Plaid will once again display the authorization form, and then submit your payment.

How it works

You should view the code for the complete details, but here's the brief summary of how Plaid Transfer works making use of Link's Transfer UI.

Already connected an account?

If your customer has made a payment in the past and has, therefore, already connected their bank to your application through Plaid, this is the overall process for making a payment:

When a user chooses to make a payment, the client calls the /server/payments/initiate endpoint on the locally-running server, passing along the account ID to use.
On the server, the application creates a Transfer Intent by making a call to Plaid's /transfer/intent/create endpoint. It includes data about the payment such as the user's legal name, the account they're using, the amount of the payment, and so on. It receives back an intent_id.
The server saves this payment information in its local database, storing the intent_id alongside the rest of the payment information.
The server then creates a link token through Plaid's /link/token/create call, sending the intent_id that it received in the previous step, along with a few new pieces of information (like the products array, the user's language and so on). It receives back a link_token, which can be used on the client to display a properly configured Link session.
This link_token is then returned to the client and the client uses the Plaid JavaScript SDK to open Link.
Inside of Link, the user is presented with a Nacha-compliant authorization form, so they can authorize the payment. Plaid stores this proof of authorization on its servers.
Once the user completes the Link process successfully, the payment is in Plaid's system and is ready to be sent off to the ACH network. We just need to make sure our application knows about the transfer that was created.
In Link's onSuccess() callback, the client sends down the original intent ID to the server's /payments/transfer_ui_complete endpoint. The server then calls /transfer/intent/get with this intent_id to get updated information about the transfer.

Two important pieces of information received in the response are a) The authorization_decision and authorization_decision_rationale, which indicates if Plaid decided to approve or reject the transfer, and b) the transfer_id which is the ID of the transfer that was created by Plaid. This is different than the earlier intent_id, and will be used to identify this payment in Plaid's system from now on.
All of this information is saved in the database and is used to populate the "Payments for this bill" table.

Need to connect an account?

If your user has not yet connected their account with your application using Plaid (or they wish to connect a new account), the process works similar to before, but with these differences:

When the server calls /transfer/intent/create, the account_id field will be null because we don't have the account_id that will be used. This is a signal to Plaid that, when the user goes through the Link flow, Link needs to prompt them to connect to a financial institution.
Inside of Link, the user is first asked to connect to a checking our savings account before they are presented with the transfer authorization form.
When Link is complete, Plaid takes the public_token that it receives in the onSuccess() callback, and sends it down to its server to exchange for an access token, like you might do with any other Plaid product. This is bundled into the /payments/transfer_ui_complete call, rather than making two separate calls.
Because our application still wants to know what account was eventually used with the transfer, our server also makes a separate call to /transfer/get, to find out value of the account_id that was used in the transfer.

1a. Paying your bill without Transfer UI

If you're interested in seeing the process for implementing pay-by-bank without using Link's Transfer UI feature, you can select the "Without Transfer UI" tab and follow the process there.

The UI should look similar to the previous one -- the user can select an existing bank or ask to connect to a new one, then they can specify an amount and pay their bill. The biggest change you'll notice is that the confirmation dialog is supplied by the application, not Plaid. Behind the scenes, the endpoints used are different, and you as an application developer will need to perform additional work to store proof of authorization.

How it works

Again, you should view the code for the complete details, but here's the brief summary of how Transfer without using Link's Transfer UI works

Already connected an account?

If your customer has made a payment in the past and has, therefore, already connected their bank to your application through Plaid, this is the overall process for making a payment:

Our client displays a dialog to the user requesting their proof of authorization. This is just a placeholder dialog and should not be considered a definitive example. We recommend reading Nacha's guidelines for payments or working with your Plaid representative to make sure you display the proper authorization language.
After that, the client makes a separate call to the /server/payments/no_transfer_ui/store_proof_of_authorization_necessary_for_nacha_compliance endpoint. This is a dummy endpoint that demonstrates some of the data you would want to store for proof of authorization. You should store this data for at least two years, and may need to provide Plaid with this information if there is a customer dispute. Again, see Nacha's guidelines for additional information.
The client then makes a call to /server/payments/no_transfer_ui/authorize_and_create with information about the transfer.
The server first creates an entry in its database's payments table for this payment. We do this to create a unique ID that we can use as an idempotency key in the next step.
The server calls Plaid's /transfer/authorization/create endpoint to authorize this payment. This call checks, among other things, that the routing and account numbers are valid, and that the user has enough money in their account to avoid running into NSF (insufficient fund) errors.

This endpoint will return a decision value of declined or approved, although Plaid will default to approving transfers if it doesn't have enough data otherwise. So if Plaid can't connect to a bank to see the user's available balance, it will be marked as approved and a note will be make in the decision_rationale field. You should check this field and determine the right course for your application.
Finally, the server makes a call to /transfer/create, passing along the authorization_id that was returned in the previous step, along with some additional information about that payment.
At this point, the payment is in Plaid's system and is ready to be sent off to the ACH network. All of this information is saved in the database and is used to populate the "Payments for this bill" table.

Need to connect an account?

If your user has not yet connected their account with your application using Plaid (or they wish to connect a new account), the process works similar to before, but with these differences:

When the user specifies that they wish to connect to a new account to make the payment, the client calls the /server/token/create endpoint on the locally-running server.
Our server generates a link_token by calling Plaid's /link/token/create endpoint, specifying ["transfer"] as the list of products that are required.
The server sends this link_token up to the client, which then uses the Plaid JavaScript SDK to open Link.
If the user successfully completes the Link process, the client receives a public_token, which it then sends down to our server (via the /server/tokens/exchange_public_token), to exchange for a more permanent access_token.
This endpoint also accepts a returnAccountId: true argument, which it uses to send back an account_d belonging to the recently connected bank. This is how our client knows which bank account to use in the upcoming transfer. In a real application, you should be using a Link flow that requires the user to select only a single account so there's no risk of ambiguation here.
We then proceed with the "Already connected to an account" flow, using the account_id that we have retrieved in the previous step.

2. Updating payment statuses

When you submit a payment, it will be marked as "Pending" in Plaid's system, meaning it's bundled up on Plaid's servers and ready to submit to the ACH network. In an actual application, it would be sent to the ACH network a couple of hours later, (where its status would change to "Posted") and then the payment will appear on the user's bank statement in a day or so (where its status would change to "Settled.")

In the Sandbox environment, this doesn't happen automatically. You will need to change the status of the transfer manually. You can either do this by making calls to the /sandbox/transfer/simulate endpoint, or by using the UI within the Plaid Dashboard.

This sample application uses the Plaid Dashboard. Next to every payment is a dashboard icon. Clicking this icon will take you to the Payment's appropriate entry in the Plaid dashboard. From there, you can click on "Next Event" to simulate the next event that normally takes place in the payment process. You can also click "Failed" to simulate when a transfer might fail (for instance, if you have an incorrect account or routing number) or "Return" to simulate when a transfer is returned (typically for insufficient funds, or if the user disputes a payment).

3. Receiving status updates

When the user's payment's status has changed, our application will need to know about that. While the Plaid API contains several endpoints to fetch the status of individual payments, the recommended way of staying on top of all changes is to call /transfer/event/sync (with an after_id value). This will fetch a sequential list of transfer events since the after_id event.

These events contain all of the information needed to stay on top of payment statuses. Most commonly, this will reflect the fact that a payment's status has changed. When a payment's status has changed, we record that information our database and update the total amount due associated with a bill. Payments that are marked as settled, for instance, can generally be considered to be completed and can be deducted from the total "amount due. However, the user can still dispute unauthorized charges for up to 60 days after the payment. We also display a "amount pending" value, which is the sum of the payments that are currently marked as "pending" or "posted".

Our code contains some logic to ignore payments that follow "impossible" state logic (for example, if a payment were to go from settled to pending) This won't happen in Plaid's event sync logic, but it can happen during development. For instance, if you were to replay a batch of events you had already processed. Our code also ignores payments that it cant find in its database. That might happen if, say, multiple developers were running separate sample applications with the same Plaid client_id.

In our application, our server calls /transfer/event/sync in response to clicking the "Perform Server Sync" logic on the client. In a real application, you may wish to make this call in response to receiving the TRANSFER_EVENTS_UPDATE webhook, which you will receive whenever the status of any event changes. Alternatively, you can simply call this endpoint on a regularly scheduled basis.

Receiving webhooks

In a normal Production environment, Plaid will automatically fire a TRANSFER_EVENTS_UPDATE webhook whenever the status of any transfer changes; the webhook contains no other information, only that the status of a transfer has changed. You may wish to have your application run /transfer/event/sync in response to receiving this webhook as a way of automatically staying up to date with any changes to your users' payments.

In the Sandbox environment, however, Plaid does not automatically fire any webhooks. Your application will need to make a call to /sandbox/transfer/fire_webhook, which tells Plaid to sent a TRANSFER_EVENTS_UPDATE webhook to a URL that you pass in.

In our application, clicking the "Fire a webhook" button will send a call to the /server/debug/fire_webhook endpoint on the server, which in turn will call Plaid's /sandbox/transfer/fire_webhook endpoint. This sends a webhook to the URL that you have specified in your .env file.

If you have a working tunnel between this URL and your webhook receiver, this webhook should be picked up by the webhook server in webhookServer.js. If the server sees that this is a TRANSFER_EVENTS_UPDATE webhook, then it will call the internal syncPaymentData() function that calls /transfer/events/sync and processes the data. (This is the same function that is called by the "Perform Server Sync" button.)

What files do what?

Here are a list of files in the application along with a brief description of what they do. Files in bold contain the code most relevant to implementing Plaid Transfer.

Files on the server

db.js -- All the work for interacting with the database is performed here
plaid.js -- Initializes the Plaid client library
recalculateBills.js -- Calculates the status of a bill based on the status of all the associated payments in our database. Your application's logic may differ.
server.js -- Starts up the server and reads in all the routes listed below
syncPaymentData.js -- Calls /transfer/event/sync and updates the payment's status based on the events it receives
types.js -- A helper file that contains a couple of enum-like objects
utils.js -- Other utilities -- currently just used to get information about the signed in user
webhookServer.js -- A second server running on port 8001 to respond to webhooks
/routes/banks.js -- List banks and accounts that the user is connected to
/routes/bills.js -- List, generate and fetch details about bills
/routes/debug.js -- A place to put arbitrary rest calls
/routes/payments_no_transferUI.js -- Authorize a transfer, and create one without using Link's Transfer UI.
/routes/payments.js -- List payments, create a Transfer Intent, and create a payment using Link's Transfer UI.
/routes/token.js -- Create a link token, exchange a public token for an access token, also does all the work around fetching and saving bank names
/routes/user.js -- Sign in, sign out, create user, etc.

Files On the client

js/bill-details.js -- Does much more than get bill details! This performs the client logic necessary to pay bills, both with and without Transfer UI. We should probably rename or split up this file.
js/client-bills.js -- Fetches and displays info about the user's bills
js/home.hs -- Handle creating in and signing in users
js/link.js -- Initialize and run Link, send the public token down to the server
js/signin.js -- Gets users, signs in users, signs out users, and calls a "signedInUserCallback" or "signedOutUserCallback" depending on the user's status
js/utils.js -- Utilities, including the callMyServer method (which communicates with our server) and functions to display dates and currency in a user-friendly way.