If you could post the error message, that would be great. I don’t remember if I ever tried importing it into Unreal with the rig. The rig was made using Blender’s rigify addon, which is probably not compatible with Unreal out of the box.
When I tried preparing it for use in VR Chat, I used Mixamo to generate the rig. That may still be doable if you export just the model to whatever format you need.