Handling successful payment processing but database update failure

With payment systems, you always need a consolidation process (hourly, daily, monthly) based on sane accounting principles that will check that every money flow is matched.

In your case, I suggest that every external async call logs the sent parameters and the received response. If you do not have a response within a certain time, you know that something has gone wrong on the external system (Stripe, in your case) or on the way back from the external system (you mention a database failure on your side)

Basically, for each async "transaction" that you spawn, you know when you start it and have to decide of a reasonable amount of time before it ends. Thus you have an expected_end_ts in the database.

If you have not received an answer after expected_end_ts, you know that something is wrong. Then you could ask for the status to Stripe or another PSP. Hopefully the API will give you a sane answer as to whether the payment went through or not.

Also note that you should add a step between 1. and 2 : re-read the database. You want to make sure that every payment request you make is really in the database, stored exactly as you are going to send it.