fix

src/rest/restreg.rs

@@ -30,7 +30,7 @@ async fn register(
         .unwrap()
         .expect("There's no trip on this date (yet)");
 
-    if !(day.open_registration || user.is_cox) {
+    if register.cox_id.is_none() && !day.open_registration {
         log::error!("{} tried to register, even though the user it should not be possible to do so via UI -> manually crafted request?", user.name);
         return Flash::error(
             Redirect::to("/"),