The first one was a multi-pack and I tried using them all as instructed, running 3.3V power pin to VCC, 3.3V GPIO to IN, and ground to ground, but setting the GPIO pin to OUT and HIGH didn't cause it to trigger, even after confirming with a voltmeter that the GPIO was in fact sending out roughly 3.3V. I think when it says that it is triggered by 3.3V it's just incorrect, or defective, or something. Had the same result with all five of them in the multipack. I only tried using the 12v power supply to trigger one of them out of curiosity, since i was not longer really concerned with burning it out, and wanted to see if anything would trigger it. Turns out the 12 volt did. So I think its range for "high" trigger just isn't correct. Also found out in this process that not only are VCC and IN switched, but the jumpers need to be on for it to work at all, which seems to contradict the "documentation."

The second one I know was 12v supply, which I had it hooked up to. I could have sworn I read in the description that it's high trigger was like 2v+, but maybe that was on a similar looking one from a different seller and I'm misremembering.

I'm going to try a third one and hope for the best. It's a bit more expensive but it has decent reviews and a more fleshed out Q&A section with someone specifically saying that 5v is just operating operating, and 3.3v is reliably triggering it for them. I'll report back in case someone else if having trouble finding a working one as well.

EDIT: the project has a 12v power supply with plenty of bandwidth left, as well as room for an additional power supply, so if powering multiple "closes" at once becomes a problem I'll probably get the 12v version and replace it with that, or add a separate 5v power supply, whichever seems cheaper/easier at the moment.

EDIT2: After reading here that powering it directly from the Pi negates the protection of the opt-isolator, I've gone ahead and cancelled the order for a 5v, and instead am getting a 12v so I can power it from my 12v power supply from the get-go.