Can't introduce qwik in a existing vanilla express project

[angel-rs]

Context

Trying to add qwik to an existing vanilla js express app & cannot get it to work.

Performed steps

1. Setup vanilla js empty project with npx express-generator
2. Run npm create qwik@latest & install dependencies (using yarn@v1 for everything)
3. Add express integration to qwik
4. Perform build
5. Manually copy the express integration code to app.js (w/ updated path references)
6. Run the vanilla express server, encounter the following error:

Error: Cannot find module '@qwik-city-plan'
Require stack: /node_modules/@builder.io/qwik-city/middleware/node/index.cjs

Not sure where this @qwik-city-plan comes from, any idea on what I could be doing wrong?
On this particular project, we really need to be able to keep the existing express backend, so starting from a new empty qwik project is not really ideal.