How does one make up two combined prayers for an excuse after their invalidity becomes apparent: Is it obligatory to combine them with the intention of combining when making them up, or is it permissible to make up each prayer separately without the intention of combining?

If a person combines two prayers in advance (jam' taqdim) due to an excuse, and then it becomes clear that the first prayer was invalid, then both it and the second prayer become invalid, and they must be repeated if there is still time, as a combined set if the excuse persists, otherwise they are to be made up (qada').

If the invalidity was only in the second prayer, then only it is to be repeated.

If one doubts the invalidity of one of them and does not know which one is invalid, both are to be made up.

When making them up after the time has expired, they must be made up in their proper order and immediately.