Authorization request fails because in some cases payment method becomes hash map instead of array

The problem

Payment cannot be initialized due API validation error.

Request

{
    "RequestHeader": {
      "SpecVersion": "1.33",
      "CustomerId": "11111111",
      "RequestId": "2b794e1d-d6eb-4c33-ae1a-31b97a5500dc",
      "RetryIndicator": 0
    },
    "TerminalId": "111111111",
    "Payment": {
      "Amount": {
        "Value": 12400,
        "CurrencyCode": "CHF"
      },
      "OrderId": "000000039",
      "Description": "Payment for order #000000039"
    },
    "PaymentMethods": {
      "1": "DINERS",
      "3": "PAYCONIQ",
      "4": "MAESTRO",
      "5": "MASTERCARD",
      "6": "PAYPAL",
      "7": "TWINT",
      "8": "VISA"
    },
    "Notification": {
      "PayerEmail": "piotr.lewandowski@madcoders.pl"
    },
    "ReturnUrl": {
      "Url": "https://xxxxxxxxxxxxxxxxxxx/de_CH/order/after-pay?payum_token=r7wYLU0S_DTmz2lNA3azpplzaHNSkEcAS-bP_dMCb0o"
    }
  }

Response:

{
    "ResponseHeader": {
        "SpecVersion": "1.33",
        "RequestId": "2b794e1d-d6eb-4c33-ae1a-31b97a5500dc"
    },
    "Behavior": "DO_NOT_RETRY",
    "ErrorName": "VALIDATION_FAILED",
    "ErrorMessage": "Request validation failed",
    "ErrorDetail": [
        "PaymentMethods.1: The field is invalid."
    ]
}

Looking at error detail and documentation (https://saferpay.github.io/jsonapi/#ChapterPaymentPage) we know that PaymentMethod should contain array of strings, thus it should look like:

"PaymentMethods": [
      "DINERS",
      "PAYCONIQ",
      "MAESTRO",
      "MASTERCARD",
      "PAYPAL",
      "TWINT",
      "VISA"
 ]

I guess problem is related to this code:

SyliusSaferpayPlugin/src/Client/SaferpayClientBodyFactory.php

Line 32 in 3f3de4d

/** @var array<string, string> $allowedPaymentMethods */

How to fix?

For example:

 /** @var array<string, string> $allowedPaymentMethods */
$allowedPaymentMethods = $gatewayConfig->getConfig()['allowed_payment_methods'];

replace with:

 /** @var string[] $allowedPaymentMethods */
$allowedPaymentMethods = array_values($gatewayConfig->getConfig()['allowed_payment_methods']);