"Sending Failed" for Sky verification

[Dave207]

Been trying for 3 days now to convert to an eSim, first  phone worked fine.  But for the other sims I have the process requires a verification code to be sent to make sure that you are requesting the change.  I just get Sending Failed everytime.  But there is nothing to say what to do next if this happens, Help bit isnt helpful and gettign frustrated.