FYI...
The change of service tool on the Starlink app and website appears to be broken at the moment. There are widespread reports on social media about customers unable to change their service plan. This appears to affect Residential, Roam, and Standby Mode. Just as one example, I had a YouTube viewer comment that they were not able to change their Starlink Mini from Standby Mode to Roam for a trip.
I think much of this stems from an update Starlink is doing to prevent Residential Max subscribers from downgrading to Residential 100 Mbps and 200 Mbps, while still keeping the Max perks (50% off Roam, free Mini rental kit). That's just my speculation.
Starlink is recommending that people put in a service ticket if you cannot change your plan. But I assume they will eventually fix this glitch before support has a chance to respond. I'm sure they are getting a flood of tickets today.
Edit - Video added about this issue: https://youtu.be/e2ndOhj84qQ