If you get this error message in spite of being a guardian of the watch, you have most probably logged in using a different number. Make sure that you are logging in with the number you used for the first time while creating the guardian's account.
Note: The guardian's number has to be different from the watch's phone number. Don't use your watch's phone number to log in.
If you need our help, send your phone number and the IMEI number of the watch to our email firstname.lastname@example.org.