Error occurred on rig: Unknown error while generating motion

• by default the cartoon model you want will be just under 3mb in Fbx without the hat... i would not add it yet
• open the Fbx in Blender [free] or whatever you use and adjust the scale to 1:1 + move the model into a center spot... not doing this step is the reason you got the first error message
• export from Blender as wavefront Obj... if you use some other app then be sure its wavefront Obj which is the standard
• upload that Obj to Mixamo and place your markers... note the hand doesn't have 5 so pick a non standard rig

I get two small errors caused by the weightmap and easy enought to fix in Blender after downloading in T pose... if you want to then add a hat \ colour and reupload thats up to you

p.s, yes of course Iclone\ 3Dexchange can fix this model or any other Mixamo rig but there are already dozens of great youtubes showing that app and I would still get my basic model into a T pose before doing any other steps

assuming you have the same build as me these are the steps I would follow

1st 3D paint no longer has Fbx because Autodesk keeps changing it and its not a true standard so you need to understand that having Fbx in your workflow = mistakes that need fixing

3D paint is a great free app for Windows users but to use Fbx you will need to download older builds... I use and recommend the 2004 build