EE is the only U.K. mobile operator to offer LTE on the Apple Watch series 3 and there are numerous reports of customers that are unable to activate the LTE.
Whilst activation can take up to two hours EE says that owners seeing any one of four error messages should not attempt to activate again, but should instead call them. If you receive one of the following errors:
Error code 019
Error code 007
This account is not ready to use with Apple Watch
Contact EE and get them to remove and re-associate a new esim on your account then follow the guide below:
Unpair your watch from your iphone
Turn the watch off and leave it for at least 3 hours
Turn off WiFi on your iphone
Pair your Watch to your iPhone and set it up as a new Watch (do not choose restore from backup)
Select add data plan when prompted.
According to a report from 9to5Mac there are currently six members of staff working their way through a backlog of hundreds of calls to EE customers.