On your phone, open 0xr.space/headset and sign in with the 6-digit code from your email. The phone shows a large code. On the Quest 3 or 3S, press Scan and look at it, press Sign in when the headset asks Sign in as you on this device, then press Allow on the phone. There is no typing on the headset.
A code lives two minutes and works once; while the page stays open, the phone shows a new one before the old one runs out. Allow is always asked, whatever network the headset is on. If two devices scan the same code it ends, and the phone says This code was scanned by two devices. Show a new one. A headset signed in this way lasts no longer than the phone's session. Quest 2, Quest Pro and Pico have no camera a page can use, so they sign in by email.
Press Allow on the phone that shows the code. Nothing signs in until you do.
Codes last two minutes. Press Show a new code on the phone if a new one did not appear, and scan again.
Open Settings, press the row with your address, then Sign in on a headset.
Yes. Press Not your headset? Sign it out on the phone, or sign it out under Devices in Account.
A scanned code never switches accounts. Sign out in Account on the headset first, then scan again.