Is that the same rig from the Tower Unite sdk? (https://www.towerunite.com/sdk/creating-characters)
Because it looks like it’s either different or you’ve modified it, you can’t move or adjust the bones in any way in Blender because when you import it, it will snap back to its original position/scale in-game and things will become messed up.
When you import the rig, you have to match the model to the bones, not the bones to the model, it can make rigging certain models awkward but that’s how it has to be done.
As for the error itself, it’s not detecting any bones so I’d say they’re either named wrongly or the mesh hasn’t been made a child of the armature or weight painted properly. Either way if you got it to import it won’t look pretty.
What you want to do is open the armature .blend file again where everything is set up for you, import your model into that, then never touch the bones position/scale/rotation etc.
You will have to re position your model to fit the bones as best as you can then continue with the weight painting again.
When you get to that stage, to attach the mesh to the armature you have to drag the object into the armature in object mode(or select the mesh then the armature then hit CTRL + P) you’ll get a popup asking for how you want it to be attached. Either by Empty weight or automatic weight painting.
Use Empty if you want to weight paint each bone yourself, or use automatic if your mesh is very close and accurately surrounding the bones, even then you’ll almost certainly need to fix up some of the weights.
I found a nice video tutorial which explains things nicely if you’re struggling with weight painting;