Add activity should be fixed

Changed type to POST in BE
Changed param type in FE API

back_end/src/main/java/hackathon/FrisbYEE/rest/SessionResource.java

@@ -133,7 +133,7 @@ public class SessionResource {
         }
     }
 
-    @GetMapping("/{id_session}/activities/add/{id_act}")
+    @PostMapping("/{id_session}/activities/add/{id_act}")
     @PreAuthorize("hasRole('coach') or hasRole('admin')")
     public ResponseEntity<?> addActivity(@PathVariable Integer id_sess, @PathVariable Integer id_act) {
         Session s = sessionDAO.findById(id_sess).get();