What is the ruling on someone who thought their fast on a day of qada’ was invalid, so they completed their fast intending to repeat it, but then it became clear to them that their fast was valid? Are they required to repeat it?

The person who rejected the intention to fast because he believed it to be invalid, then his compensatory fast is void, and he must make up another day. However, if he hesitated about breaking the fast and did not reject the intention to fast, then his fast is valid according to some scholars, while others ruled it invalid. It is more prudent to make up this day to avoid the اختلاف (difference of opinion) among the scholars.