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src/components/structures/auth/Registration.tsx

@@ -224,6 +224,7 @@ export default class Registration extends React.Component<IProps, IState> {
                     flows: e.data.flows,
                 });
             } else if (e.httpStatus === 403 || e.errcode === "M_FORBIDDEN") {
+                // Check for 403 or M_FORBIDDEN, Synapse used to send 403 M_UNKNOWN but now sends 403 M_FORBIDDEN.
                 // At this point registration is pretty much disabled, but before we do that let's
                 // quickly check to see if the server supports SSO instead. If it does, we'll send
                 // the user off to the login page to figure their account out.