I assumed you would re-add the armature as the parent to the mesh, & select automatic weights, via right-click.
Edit: select the mesh first, then shift click the armature second, then right click.
You could also just manually weight paint that bone, but this is only practical for every low bone counts. Manual weight painting is best for just cleanup from automatic weighting.
Either got me an assigned armature with weights.
Also, yes the name of the action goes in the first arg of beginAnimation.