Your doing nothing wrong mate, I have the same issue as have many others using the 7 Pro. A cracking product release.
I'm not on a beta.
Yes this is annoying as just found this issue out myself. The information states that it should be supported now, but that is clearly wrong.
I have the same problem, it appears to not work.
Heres an invite code ....enjoy whoever gets it first!
I bought the OnePlus clear one too. Seems fine for the money, but like above poster states might be a bit slippy.