Error on splash screen if sync is failing

Display an error on the splash screen with the spinner if the sync
request is not working, rather than just sitting there with a spinner
as if nothing is wrong.

Fixes https://github.com/vector-im/riot-web/issues/7148

src/utils/ErrorUtils.js

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { _t } from '../languageHandler';
+import { _t, _td } from '../languageHandler';
 
 /**
  * Produce a translated error message for a
@@ -48,3 +48,31 @@ export function messageForResourceLimitError(limitType, adminContact, strings, e
         return _t(errString, {}, extraTranslations);
     }
 }
+
+export function messageForSyncError(err) {
+    if (err.errcode === 'M_RESOURCE_LIMIT_EXCEEDED') {
+        const limitError = messageForResourceLimitError(
+            err.data.limit_type,
+            err.data.admin_contact,
+            {
+                'monthly_active_user': _td("This homeserver has hit its Monthly Active User limit."),
+                '': _td("This homeserver has exceeded one of its resource limits."),
+            },
+        );
+        const adminContact = messageForResourceLimitError(
+            err.data.limit_type,
+            err.data.admin_contact,
+            {
+                '': _td("Please <a>contact your service administrator</a> to continue using the service."),
+            },
+        );
+        return <div>
+            <div>{limitError}</div>
+            <div>{adminContact}</div>
+        </div>;
+    } else {
+        return <div>
+            {_t("Unable to connect to Homeserver. Retrying...")}
+        </div>;
+    }
+}