As mentioned before, I don't use Unreal so most of my knowledge on Unreal is second hand, but this is all I can give you regarding that error, I hope this can help you fix it:
https://forums.unrealengine.com/t/mesh-contains-root-bone-as-root-but-animation-...
https://forums.unrealengine.com/t/error-mesh-contains-hips-bone-as-root-but-anim...
Is it perhaps feasible for you to provide the animations along with a freely available and royalty-free mesh or model, akin to the approach on platforms like Mixamo? I've attempted the tutorial without success and subsequently explored Fiverr to enlist someone's assistance in resolving the issue. However, two sellers conveyed a similar message—stressing the need for a mesh for successful conversion to Unreal Engine. Both noted that the existing bones are not humanoid, leaving me somewhat perplexed and finding the process rather challenging.
If you could assist in reconfiguring the animations onto a model, I would be inclined to approach Fiverr's 3D artist sellers to retarget them for Unreal Engine. Following this, I could provide you with the models. This approach would potentially enhance your sales, as the models would officially be compatible with Unreal Engine.
