No idea why the Starlink website won't recognise the short Plus Code, especially when it shortens the full code if I put that in :P. Your area code is "9C9J",

No idea why the Starlink website won't recognise the short Plus Code, especially when it shortens the full code if I put that in :P. Your area code is "9C9J", making your full code "9C9JJQX3+84". As an aside, plus codes should be wonderful things but the tooling isn't particularly well built out -- this is the first application I've seen using them that's not Google Maps, and it's not worked as well as I'd hoped it would :(. In this case, the geocoder for the area hasn't done what it ought to have done. And I fear that while the full codes don't need a geocoder, short codes might be generally susceptible to incompatible geocoders leading to incompatibilities between implementations. Which is what we seem to be seeing here.