Tim Hunt

I don't know the answer to your qustion, but this web service is used by the Moodle moodle app, and it works there, so one way to solve this would be to attempt the quiz in the mobile app in a way that lets you inspect the network traffic, to see what the right request is.

If that is what is going on, then this quiz design technique would help: https://docs.moodle.org/404/en/Effective_quiz_practices#Robust_testing_with_random_variants. That is also a good way to make oneline quizzes for many other reasons than just this one threat.

Note that M.util.set_user_preference is old and deprecated.

These days you should use the core_user/repository JS module:

import {setUserPreference} from 'core_user/repository';

setUserPreference('preference_name', status);

(Bear in mind that is an async function.)

I think the words you are looking for is "Extra credit". https://docs.moodle.org/404/en/Grades_FAQ#Weights_and_extra_credits