A Concern About Prayer Validity: What to Do Next?

As-salamu alaykum, I was wondering if anyone has been in a situation where they found out their prayer was invalid or they were praying incorrectly after they had already completed it. Do you still have to redo the prayer in this case? I'd love to hear some advice on this matter, insha'Allah. Maybe someone can share their experience or some knowledge on how to handle such a situation. Jazakum Allahu khayran for your help and guidance.