How to handle copay that was reimbursed by FSA and later fully covered by health insurance? Can you get a credit with the medical provider to use for later that year?

Scenario: You pay $50 for a medical copay at your appointment and and then submit to your FSA and get reimbursed. After your insurance processes the claim, unexpectedly, they end up covering the full amount and pay the medical provider fully including the copay that you already paid. What are your options? If you ask for a refund from the medical provider since insurance covered the copay, then you are getting $50 extra from them. Can you return the $50 to the FSA? Or can you ask the medical provider to keep the $50 as a credit and then use that money for a medical expense later that year and then no action is needed with respect to the FSA? And/or as long as medical expenses for that year exceed the amount you put on the FSA card, it doesn't matter?