I would strongly suggest you try to find the manual for the handset in order to understand if you can overcome the call-before-unlock issue. There may be a link you can add which will disable the call-before-unlock behaviour.
Out of an abundance of caution, randomly connecting 12V to the wrong terminal could cause issues… I know the guy from the company that maintains our intercom system wasn’t too enthused about having “normals” fiddling with the intercom wiring precisely because it could mean transformer power is accidentally shorted to the wrong terminal and result in an expensive repair to the entry panel. 
Unfortunately we don’t know what the app suggested for the wiring for this handset as it’s not online (and I don’t plan on reinstalling my Ring Intercom just to find out!) - can you post the wiring screenshot from the app?
I’m not suggesting you go ahead and fiddle with your wiring, but based on the reverse engineering of the A harness in this post
then maybe the following wiring is close to what you need (these are the same 4 A-wires used on my Came/BPT Sytem 200 “AGT A200K” handset - compatible with the C200)
A3 → 1 Mic (Speech Out)
A2 → 2 Speaker (Speech In)
A1 → 3 0V
A6-> 4 12V DC