Octopus outgoing meter readings

I’ve finally got all my paperwork in place for being paid to export.

I’m signed up with Octopus Outgoing, and they’re now asking for a meter reading! I’ve got a smets2 smart meter, so it’s a bit incongruous, but whatever.

However, which reading do they want?

Sorry if this is a bit off topic. I don’t know where else I might find someone who’s been through the same, and their helplines are closed for the weekend.

I’ll answer my own question, the correct place to look was here: