Could not find bind pose

I know almost nothing regarding 3D modelling. But I have some weapons and such that need a basic skeleton (for attaching it to the players hands and for spawning the Muzzle). So I just fired up Blender, added a single armature and matched the armature scale to the mesh-scale and then exported it.

I’m getting the warning:

I’m not sure if this warning affects me since I’m not really gonna be using the mesh for animations or anything.
Everything does seem to be working fine though. I have a skeleton and I can create my dummy Muzzle-socket: