I am unable to drag a weapon or amo into the turret. If i use the NPC option this loads an NPC turret with no problems.

I'm not sure what would cause that off the top of my head. Did you have building privilege when trying this? If not, maybe try with building privilege to see if that works. There is no special code in the plugin that allows or prevents dragging items into the turret, and it works the same as Modular Car Turrets, for which nobody ever reported this problem.

Could you try placing a turret next to the drone to see if you can place weapons and ammo in it? Can you also try placing different kinds of weapons in case it's only specific ones?

I was able to load the regular drone turret with a weapon and ammo no issues.  NPC turret will not allow you to add anything.

FYI you are not supposed to be able to add items to the NPC turret since they are a static prefab.

As for the OP's issue, if you have a plugin that automatically turns on the turret when deployed, you will have to flip the switch on the back to turn it off to add weapons and ammo.