I Found Out All of My Past Prayers Were Invalid, do I need to repeat them?

Assālamu ʿalaykum wa raḥmatu-llāhi wa barakātuh. For the past month, I have been reciting all of my prayers silently in my head but only just found I am supposed to recite them out loud. Do I have to make up these prayers or am I forgiven for not knowing? Thank you and jazakallah khair.