Payment Shows Success But No Payment Record in Salesforce

The Payments web page shows that a payment was made successfully and the payment appears in the payment gateway (Stripe, QB) but no Payment record is created in Salesforce.

This can happen when the Payments web app is trying to create a Payment record in Salesforce but there is an issue in Salesforce preventing it due to configurations. For example, there is a Flow error unrelated to the Payment app that prevented the Payment record from being saved to the database. Or, a user created a required field on the Payment object.