Re-register for a scalar token if it expires
It looks like Fractal has sticker support, which means it also has a scalar_token registered. These tokens can become invalid at any time, so clients need to refresh their token if it has expired. See also: https://github.com/vector-im/riot-meta/issues/279
Both the API to check a token and the fact that they expire are undocumented, but this should be fixed alongside https://github.com/matrix-org/matrix-doc/issues/1286
For now though, Fractal should make a request to
https://scalar.vector.im/api/account?scalar_token=YourToken before passing the token off to the sticker picker/calling an API. If it receives 200 OK, the token is okay. 4xx or 5xx response codes indicate it is not valid.