Identity service specification uses a wide range of casing for endpoints

Namely:
* `/store-invite` (hyphen)
* `/requestToken` (lower camel case, used and documented elsewhere in the Matrix Spec)
* `/isvalid` (lowercase)

Additionally, it is the only API that has `/api` in the route.

Start in the Identity Service portion of the Matrix specification and compare the documented /store-invite, /requestToken, and /isvalid routes with other Matrix Spec endpoints. Check the rationale for the /api prefix and existing casing conventions before proposing a consistent specification update. Done means the routes and their documentation follow an agreed convention.

Written by the indexing model from the issue text.