Better error messages for when features are disabled on a users HS

[ninchuka]

Your use case

What would you like to do?

have more descriptive errors on why something is not working, such as adding a phone number in element on matrix.org

Why would you like to do it?

to reduce the amount of people asking about why something isnt working with a cryptic error message

How would you like to achieve it?

have a way for the app to know if something is disabled on the HS and to share that to the user easily when they try to use such feature thats turned off

Have you considered any alternatives?

No response

Additional context

No response

Are you willing to provide a PR?

No

[aaronraimist]

Example: Currently users see

Limit exceeded for this country

when trying to attached a phone number to a matrix.org account which doesn't really explain the situation https://matrix.to/#/!YTvKGNlinIzlkMTVRl:matrix.org/$AtnUGtmHXWiMuAtK3hvquiP90PPJ87y9qAI-ZEaRQ7U?via=matrix.org&via=privacytools.io&via=mozilla.org

https://github.com/matrix-org/sydent/blob/cc9d46d9c2502c7ea62218eb617e9785282ebf2f/sydent/http/servlets/msisdnservlet.py#L125

[csharper2010]

I get error when trying to add phone number even if identity server vector.im is set up:

MatrixError: [500] Internal Server Error (https://matrix-client.matrix.org/_matrix/client/r0/account/3pid/msisdn/requestToken) (Status 500)