CryptoTap common wire?

[Bricks]

Hi guys!
I hooked up Tap to pay on my autocashier and it was easy with the receptacle inside. Now I’m trying to install them in the SS.

I put the meter on Ac and one lead on the black wire, one lead on the metal box... got 24 volts ok.

Then I set the meter on continuity and I’m not sure if I’m supposed to check from the wires to the metal box or not.
Could anyone tell me how to find the common?

 

[MEP001]

The red wire to the Dixmor is hot, the green is common. You'll have to follow back to the wire nuts from the timer.

 

[Bricks]

The red wire to the Dixmor is hot, the green is common. You'll have to follow back to the wire nuts from the timer.

Thank you once again, sir!!
It’s up and working!