It looks like you are searching via user_id which is API v5, so ensure you add ‘&api_version=5’ to the end of your API call (there may be a better way to handle it in AJAX but the above should work.)
It looks like you are searching via user_id which is API v5, so ensure you add ‘&api_version=5’ to the end of your API call (there may be a better way to handle it in AJAX but the above should work.)