Nginx – The provided key 'sk_test_***' does not have access to account 'cus_PN***' (or that account does not exist). Application access may have been revoked

I am trying to figure out why I seem to be getting this error when trying to call a Stripe API. The error I am getting is this:

The provided key 'sk_test_***********************************************************************************************JQQa' does not have access to account 'cus_PN***' (or that account does not exist). Application access may have been revoked

And my code is as follows:

        const stripe = require('stripe')(
           process.env.STRIPE_REAL_API_SECRET_KEY || process.env.STRIPE_TEST_API_SECRET_KEY
       );

       const eligibleBalanceDueData = res[1].rows.map((row) => ({
           balanceDueId: row.balance_due_id,
           affiliateStripeId: row.stripe_customer_id?.trim(),
           totalAmount: parseFloat(row.total_amount),
      }));

      for (const item of eligibleBalanceDueData) {

       // Retrieve the Connected Account ID associated with the Customer ID
            const connectedAccountId = await stripe.accounts.listExternalAccounts(
                item.affiliateStripeId,
                { limit: 1, type: 'custom_account' }
            );

            const transfer = await stripe.transfers.create(
                {
                    amount: 2, // item.totalAmount * 100, // Amount in cents
                    currency: 'usd',
                    destination: connectedAccountId.data[0].id,
                    transfer_group: 'affiliate_payout',
                },
                {
                    idempotencyKey: 'unique_key_here'
                }
            );
      }

It seems that if I have any of the above Stripe API calls (i.e. await stripe.accounts.listExternalAccounts or await stripe.transfers.create) then I get the error.

This is supposed to be code to pay affiliates, which are set up as customers in stripe. So I guess technically I just want to be able to send a customer a payment via the API. If I am correct, I assume that transfers are what should be used in my case, not payouts or paymentIntents, and that the destination in the transfer call should be the account id of the stripe customer id.

Valid API Key:
I have checked the secret keys (in test mode), and by the stripe dashboard it says "Standard keys – These keys will allow you to authenticate API requests". I assume the secret key is therefore valid, presumably with full permissions and has no issue.

Valid Account:
The account in the error (i.e. 'cus_PN***...') does exist (i.e. there is a customer with that id) – and the value is stored inside item.affiliateStripeId.

Access?
I assume that the Api calls should work with item.affiliateStripeId, because it’s a customer.

I assume this code will create a test payment rather than a real payment.

Stripe API Response:

{
  type: 'StripePermissionError',
  raw: {
    message: "The provided key 'sk_test_***********************************************************************************************JQQa' does not have access to account 'cus_PNaqkPyNm7hjp4' (or that account does not exist). Application access may have been revoked.",
    type: 'invalid_request_error',
    code: 'account_invalid',
    doc_url: 'https://stripe.com/docs/error-codes/account-invalid',
    headers: {
      server: 'nginx',
      date: 'Tue, 16 Jan 2024 09:11:48 GMT',
      'content-type': 'application/json',
      'content-length': '432',
      connection: 'keep-alive',
      'access-control-allow-credentials': 'true',
      'access-control-allow-methods': 'GET,HEAD,PUT,PATCH,POST,DELETE',
      'access-control-allow-origin': '*',
      'access-control-expose-headers': 'Request-Id, Stripe-Manage-Version, Stripe-Should-Retry, X-Stripe-External-Auth-Required, X-Stripe-Privileged-Session-Required',
      'access-control-max-age': '300',
      'cache-control': 'no-cache, no-store',
      vary: 'Origin',
      'strict-transport-security': 'max-age=63072000; includeSubDomains; preload'
    },
    statusCode: 403,
    requestId: undefined
  },
  rawType: 'invalid_request_error',
  code: 'account_invalid',
  doc_url: 'https://stripe.com/docs/error-codes/account-invalid',
  param: undefined,
  detail: undefined,
  headers: {
    server: 'nginx',
    date: 'Tue, 16 Jan 2024 09:11:48 GMT',
    'content-type': 'application/json',
    'content-length': '432',
    connection: 'keep-alive',
    'access-control-allow-credentials': 'true',
    'access-control-allow-methods': 'GET,HEAD,PUT,PATCH,POST,DELETE',
    'access-control-allow-origin': '*',
    'access-control-expose-headers': 'Request-Id, Stripe-Manage-Version, Stripe-Should-Retry, X-Stripe-External-Auth-Required, X-Stripe-Privileged-Session-Required',
    'access-control-max-age': '300',
    'cache-control': 'no-cache, no-store',
    vary: 'Origin',
    'strict-transport-security': 'max-age=63072000; includeSubDomains; preload'
  },
  requestId: undefined,
  statusCode: 403,
  charge: undefined,
  decline_code: undefined,
  payment_intent: undefined,
  payment_method: undefined,
  payment_method_type: undefined,
  setup_intent: undefined,
  source: undefined
}

It seems to link to this: https://stripe.com/docs/error-codes/account-invalid – "The account ID provided as a value for the Stripe-Account header is invalid. Check that your requests are specifying a valid account ID."

To be honest, I am completely lost here, especially after reading the docs and other posts. Any help would be greatly appreciated.