If a person prostrates on something that is not valid for prostration due to ignorance of the ruling and…

Answer

In the name of Allah, if the person prostrates on something that is not valid for prostration, believing that it is permissible, and realizes this after raising their head, they must repeat that prostration, even if the mistake was in both prostrations. They must also repeat the prayer. If they realize it during the prostration, they must move their forehead to a valid place for prostration and should not raise it. If they raise it intentionally and place it on a valid spot for prostration, their prayer becomes invalid. However, if they cannot move their forehead, and the realization happens before completing the required remembrance, they should finish that prayer and then repeat it. Similarly, if they realize it after raising their head from prostration, they should complete the prayer and then repeat it. Allah knows best.