Hello, I wanted to add addons / mods to my realm and when I try I get an error that says they could not be saved because they are incomplete.

Hello, I wanted to add addons / mods to my realm and when I try I get an error that says they could not be saved because they are incomplete. I also get the error when I try to add them to the realm world, it simply says "error ..." and I have tried several things, but they do not work for me.