The money returns to your balance and retries in the next run. Usually a bank detail that needs correcting.
Nothing is lost. A failed payout returns to your balance and is included in the next run automatically. You do not need to ask for it.
Why it happens
Almost always the bank details: an account closed, a number entered wrongly, or a bank refusing a transfer type. Your bank tells Stripe, and Stripe tells us.
What to do
Check your payout details in your Stripe setup and correct anything wrong. If they look right, your bank will know why the transfer was returned — Stripe passes on the fact, not the reason.
You are told
An email and a notification, both times: when it fails, and when the retry succeeds. Money moving is never something you should have to discover by checking.
If it fails twice
Contact support rather than waiting for a third attempt. Two failures with the same details will produce a third.