Handle must be a BasePart, if you don’t want a handle you can toggle off RequiresHandle; in this case just naming a part Handle and welding the other parts to that handle should fix it.
The handle has to be a part, it can’t be a model. You can fix that easily by just naming the hilt of your weapon Handle and welding the other pieces of the weapon to it. If you’re not familiar with welding there’s plenty of plugins that make it quite easy to do.