By default the multiplayer mode uses weapon factories, when you run over them, it picks up that weapon, if you already have it, it adds ammo, Quake 3 Arena/Unreal Tournament style. However you can still implement the press E to pick it up mechanic.
The SpawnedWeapon is a Replicated_WeaponBase actor reference (you can promote “self” to variable).
3. Add Replicated_WeaponBase child classes into the level.