Unable to upload simple FBX model to Mixamo

Hello,

I have a simple human model, set in a basic T-Pose, and am exporting it from Cinema 4D on a WIndows 10.

I am exporting the model as both an FBX and an OBJ (no lights or textures or anything; just the model's geometry), but either one is having a hard time uploading to Mixamo. The export size is normally around 90MB.

Half the time it doesnt make it through the intitial upload process. When I do, I set the rigging points (chin, knees, etc) then I hit "Next." The auto-rigging tries to figure it out, then gices me a "sorry" error message, or just brings me back toi the rigging points page without an explaination why.

I have tried exporting the model made of seperate peices, as well as baking it into one solid peice of geometry, but I am getting the same errors either way.

Anyone have a good solution or have encountereed this before?

Thanks!