So on my Model S I can trigger autoparking whether forward or backward by double pressing on parking button. For Model 3 that doesn't work. Why? Is there an equivalent combo?
This equivalent doesn't seem to have made it to the 3 yet. Currently, you have to identify a spot, drive VERY SLOWLY past it until the P icon pops up, put the car in reverse, and then a "start" button comes up on the screen to press. As I also understand it, in the S, you could leave the car after double pressing? Not an option in the 3 at this time. If that's not correct on the S, sorry....I don't have one, but it was something I'd read.
Um. Drive slowly, wait for the "P" symbol to appear on the screen, tap that, then put into reverse, remove hands?
That feature is actually Summon, not Autopark, which works as @Tronguy said. The Model 3 manual says you can use the Park button to initiate Summon from inside the car — are you sure you’ve disabled the “Require Continuous Press” option in the Summon settings?