Sorry for reviving a 3-month-old thread, but this turned up first in a Web search, so I thought I should share my recent experience....
I recently bought a new phone (a Pixel 6 Pro), and it arrived today. Things started out well (Google has made the transfer of data from an old phone very easy), but it went downhill from there. After
seeming to pair as a key, the new phone failed to work when I actually wanted it to, and I ended up deleting the Tesla app (multiple times), re-starting the phone (multiple times), restarting the car's computer (multiple times), and it still wouldn't work. I tried the
procedure above and it didn't work. At different times, the option to set up the phone as a key disappeared from the Tesla app or failed with a "disconnect other paired devices" message. This was infuriating, because I didn't have anything else I'd paired with either the car or the phone with me. In frustration, I set off to my nearest Tesla store to see if they'd have better luck. When I was a couple miles away from the store, I realized that the "other paired devices" might have referred to my old phone, which, although it was not with me in the car, was likely within Bluetooth range in my house. Sure enough, when I pulled into the parking lot, the new phone paired and worked when I tested it. Tesla could be more specific about this in their error message. Time will tell if the phone-as-key works in the future....
Anyhow, if somebody else finds this thread in a Web search and is having similar difficulties, my suggestion is to turn off all other phones that are paired with the Tesla, or at least disable their Bluetooth. My hypothesis is that the Tesla needs a clean signal from
one phone to set it up as a key; any others may interfere with that operation.