Ik this post is a bit old, but it’s worth pointing out that Octopus won’t validate an export MPAN until the DNO has updated ECOES with the new technical details, and sometimes that update lags behind the G99 approval even when Grid say everything looks fine. In my case, the installer and DNO both said all good, but the ECOES record still showed the site as import-only, so Octopus’s system auto rejected it twice. Once the DNO repushed the export MPAN into ECOES, Octopus processed it within a week and backdated payments. If u haven’t already, i’d push specifically for a screenshot or written confirmation of what ECOES actually shows for ur site, rather than relying on what each party says separately. Hopefully this helps someone who encounters smth similar