Octopus Go API not accepted

Trying to connect ny Octopus Go account to the smart tariff but my API not being accepted. Error mesage is 'The given data was invalid'

Any ideas?

Thanks

I sometimes have to put either the import or export MPAN in to get it to work.
Seems to make a difference, but don't know why. Other users have reported the same.
Check out other posts on here about colons or not on the end of the API