2015 Prius 2 rear caliper piston won’t retract

You want the raised spoke pattern on rear caliper piston face oriented like an “X”. This will put the spokes on either side of the stubby pin on pad backing plate, which is imperative.

 

Look how the pad with the two pegs stick out. If you set that pad against the caliper, as it will
align against the rotor, you will see how to turn the puck. I believe they are at the top and bottom.
But it doesn't matter. If you line it up you will see the two spots those pins go in.
I'm certain Mendel will provide pictures and the history of it soon.
But if you search for rear pad alignment on here, it will pop up.

 

Besides correct alignment, you want to make sure it STAYS that way:

1. Assemble everything, don’t apply parking brake.
2. Push brake pedal 5~6 times, till it really firms up.
3. Reconnect neg 12 volt battery cable. (This should be disconnected prior to any disassembly)
4. Take short test drive, taking it easy on brakes.
5. Return home, park on level ground, apply and release parking brake several times.
6. Raise rear of car enough for wheels to be clear, and test spin them. They should go 2~3 revs with a push.

 

This