Issue setting up cellular with Telstra

I recently bought a refurbished 8th Gen. I’m trying to set up the cellular but I’m having an issue.

I’m in Australia & with Telstra postpaid. I’ve got the option to add it to my plan so I follow the instructions. After I verify my ID via the Telstra app, the watch app says it’s done but then I get this error message. Telstra isn’t much help as they say I need to set it up through the watch app. I’ve been trying for 2 days now.
Any suggestions?

u/minionofthenight — 2 months ago