In Main Weapon Gun Type, you need to connect the Main Weapon Current Ammo node to the Spawn Actor.
Wait, that’s impossible. There’s nowhere for me to connect it to!
You don’t have it set up for this yet. You need to go back to the BP Master Pickup and tick Expose the Main Weapon Current Ammo on spawn. You can now connect up the Main Weapon Current Ammo node to the Spawn Actor.