Everything I’ve read indicates that this should “just work” but it didn’t for me. I got a pop-up that indicated I needed to open a help ticket!
The N6 had been on Project Fi and when I dumped that service it was not supported on RW so I ordered a 5X. I don’t think more than a week passed before support for the N6 was added to RW.
There are things I like about the 5x and other things I like about the N6, so swapping back and forth would be handy based on what I am doing at the time. Also to use one as a spare.
Fortunately I did not go through with the help ticket advice and just put the SIM back in the 5x and it works still.
Either I missed a step or the instructions need to be clarified.
Note: the N6 has been fully cleared (reset) since I left Project Fi and I’ve just been using it as a WiFi device since then.