5E Ammo Tracker does not work

I am pretty sure I have it all set up properly... it is turned On in my game Settings, and it is turned On in the character sheets. The Bullets entry in inventory is checked "Use as a resource" and the gun is checked "Has an Attack". Under the gun in the Attacks, I put "Bullets" as its Ammo. Still I get nothing. Am I missing something?

Pretty sure you need the Api which requires a Pro account.

AMMO TRACKING:OnOffProvides automatic ammo tracking with the 5th Edition OGL by Roll20 Companion API Script.

Ah. Well I am merely Plus, so that explains it. Yet another irritating detail which frankly should be free.