Avoid duplicate wwwroot

user-binding.php

@@ -23,5 +23,5 @@ $isTeacher = has_capability('mod/labnbook:addinstance', $context);
 $role = ($isTeacher ? 'teacher' : 'learner');
 global $USER;
 $url = $fetchInstitution->getRedirectUrl();
-$token=$fetchInstitution->getBindingTokenForRedirect($CFG->wwwroot . $returnUrl, $role, $USER);
+$token=$fetchInstitution->getBindingTokenForRedirect($returnUrl, $role, $USER);
 redirect($url."?token=".$token);