Can't get setFieldValue to work
If you are going to set the fieldValue, you need to save the element:

    $userObject = Craft::$app-&gt;users-&gt;getUserById($userId);
    $userObject-&gt;setFieldValue('discountPercentage', 15); 
    Craft::$app-&gt;elements-&gt;saveElement($userObject);


Should do the trick.