The following scenarios exist for failed payments:

You can see exactly where the problem is in the status of the payment process.

for example if the status "Contestation lost" the best thing is to do is to contact your customer because the bank account may not be covered.

In the 3rd case, check the user's payment at Stripe for the mandate reference.

Then send the link you can find in the Payment Method in Stripe to the user concerned (this is your direct debit mandate). The user sends the link to their bank with the instruction to agree to it.

Here you find general and important information about accepting payments for memberships with Stripe.