Rachio 3 won't trigger pump relay - Rachio 1 worked fine

Having problems with my Rachio 3 “upgrade”. As soon as I try to run a zone I get a red light. I hear the relay click briefly, but doesn’t stay latched. Voltage across relay coil drops to 0.4vac, but is 24vac with nothing connected. Relay is Hunter PSR-52.

Rachio 1 worked fine. Rachio 3 can’t trigger the relay. Way past return window, so do I need to pitch the Rachio 3 in the trash bc they made it cheaper than the 1? Or is mine just defective?

Already super disappointed at the small diameter of the flow meter. Really don’t want to shrink my plumbing down from 1.25" to 3/4" even though I am well within the flow specs. Beginning to think Rachio is too down-market.