"Unknown Error" when trying to rig imported model

[EltonJohnisPlumpandDreamy]

When I load my custom character into Mixamo and place the points, I get a message saying "Unknown Error while generating motion."  It's like Mixamo doesn't recognize my model as a riggable character.  I realize it may be hard to tell from just a screenshot, but on first glance can you tell what it is about my model that is causing issues?  The thumbs look reversed here, but they are correctly positioned. Also, I tried this model with different hands, thinking they were the problem--but no results.  Granted, it's clumsily built. But I just ran this off as a prototype for something in AR. Wondering if my construction method in C4D is the problem, but I haven't had too many problems so far.

[Ussnorway]

the thumbs are correct mate which means your file (assume Fbx) is reading wrong and turning the head around to face behind... I would convert this model to wavefront Obj, upload that to rig the bones and adjust my work flow from that point

[Edelplastic]

What if he need FBX for his Engine? Not every Engine is compatible with OBJ. So in fact, your answer isn´t helpful bcse it not solve the problem.

[Ussnorway]

if he needs Fbx he can have it because Mixamo will download the model as Fbx [many different choices]

uploading as Obj is a good work around because its a standard file type... wavefront Obj is best and this thread is over a year old so its likely that was the issue

[Mistyre]

i get the same error but with an obj file