How do I equip attachments in unturned? [PS4]

Recently started playing Unturned, found a couple of helpful starter guides, and got a decent gun. Got a few attachments for it, but I cant figure out how to attach them? Everything I've seen says you select the attachment in your inventory, press square, and the option is supposed to be there, but none of my attachments give me the option. I have verified that these attachments are supposed to be able to go on this gun. To clarify, I am using a Sabertooth, and attempting to attach a Military Barrel, 7x Scope, Vertical Grip, and Rangefinder. The attachments only give the option to drop them, nothing else. The gun has the option to Equip, Strip, Drop, Repair, and Salvage it. Nothing about attachments. Am I missing something? I am playing on a PS4.