The api.sky.blackbaud.com/school/v1/users/{userid}/customfields endpoint seams to be modifying the wrong user's custom field. E.g. running a POST request on a user will create the new custom field under the user running the POST request, not the user with the user_id in the URL. The same thing happens with PATCH requests but in this case SKY seems to ignore the provided id and modifies the first id with the same field_id under the user making the request.