Summary
Cause
EXAMPLE: You have your Stripe account setup in Sage Accounting. Typically, you would submit an invoice to your client, which will have the payment link associated with it. This way when they use the payment link from the invoice, the Invoice will also be marked as paid in Accounting.
In this particular example, everything is fine, you don't need to allocate the Stripe transaction with the Invoice in Sage. But it happens that the client fails to use the payment link in the invoice, or they submitted you a payment to your Stripe via a different method. In that case, you are looking to allocate the Stripe payment with the outstanding invoice in Sage.
Resolution
In Sage Accounting, you can not manually allocate stripe transactions to an outstanding invoice. Your customer has to have paid using the PAY NOW link on the invoice you sent them. This way, both the payment and the outstanding invoice will get associated automatically.