A couple months ago, I had a dental appointment and, since my dentist is not in-network, I had a substantial bill. I submitted this expense to my flex spending account (FSA) for reimbursement, and I was reimbursed in full. A few weeks later, however, I received a check from my insurance partially covering the original amount.
I have not yet deposited the check from my insurance, and it seems like it might be unethical to do so. What is the proper thing to do?