Can't upload .ttf or .otf fonts to CC library

I am working in Illustrator across multiple devices, and I want to put these fonts on CC so I can use them on my iPad. When I try to upload a .ttf or .otf file to CC, I get this error message:

From my understanding, these file types should be accepted. I downloaded them from free online libraries over the years, so could it be a restricted rights issue? I have attempted multiple fonts and they all get the same error message.