Mirrored rig doesnt affect mesh

Hey guys I hope you can help me out.I was following this tutorial on how to modify mixamo rigs to make my own animations (https://www.youtube.com/watch?v=_bZR2BJGN_c) but unfortunately he only does one side of the rig. I tried duplicating the left side and mirror it over to the right side and the rig works as intended, but it doesn’t affect the mesh.why would that happen?

Found the issue. I forgot to give my bones the appropriate names (Right and left)