Downloaded and installed the most recent version here, loaded up minecraft with nothing in the mods folder.

upon trying to connect I got this:

Tried downloading previous versions and installing them, no effect.

When I run the non-rift version of 1.13.1 it works flawlessly.

I'm not even sure what the issue with this is, but I would like to be able to load my mods. Thanks for any help provided.

That's because Rift isn't 1.13.1.........Rift is only 1.13 for the moment. Closing the issue as it is not an actual issue.