Why is Loop telling me to add my smart meter again?

This can be caused if you couldn't complete validation via bank card and instead had to enter your In Home Display code. After entering this code, if you didn't click on “Return to provider” on the final stage of authorising with N3rgy then Loop won't know that you’ve fully authorised the meter. 

To solve this, re-enter your address and MPAN, go through to the N3rgy site and accept their terms and enter your code. Then press “Return to Provider”. Your smart meter should now be registered with Loop.