Getting error on applying UDID as "Please enter a valid UDID"
It sounds like you're getting the wrong number for the UDID. My process for doing this is to:
- Connect the phone I want to add to my Mac while I have Xcode running.
- Agree on the phone I can trust this computer and put in my passcode to verify that.
- Open up "Devices and Simulators" window in Xcode from the Window menu.
- Copy the number with the label "Identifier" and use that in the Apple developer account portal.
If you have a paired Apple Watch, it'll show on the same Devices screen in Xcode as the phone it's paired with in the section just below the header.
I hope this helps.