The rating works. The JSON response looks like this:
<br />
<b>Warning</b>: Invalid argument supplied for foreach() in <b><path>/wp-admin/includes/plugin.php</b> on line <b>1422</b><br />
{"status":"success","data":{"sequence":"1","post_id":"58","html":"<span class=\"rating-result rating-result-58 mr-filter\"><span class=\"mr-star-rating\" style=\"color: #dd0404 !important;\"><i class=\"fa fa-star mr-star-full\"><\/i><i class=\"fa fa-star mr-star-full\"><\/i><i class=\"fa fa-star mr-star-full\"><\/i><i class=\"fa fa-star-o mr-star-empty\"><\/i><i class=\"fa fa-star-o mr-star-empty\"><\/i><\/span><span class=\"star-result\">3\/5<\/span><span class=\"count\">(1)<\/span><\/span>","rating_result":{"adjusted_star_result":3,"star_result":3,"total_max_option_value":5,"adjusted_score_result":3,"score_result":3,"percentage_result":60,"adjusted_percentage_result":60,"count":1,"post_id":"58"},"hide_rating_form":true},"message":"Your rating was 3\/5.","validation_results":[]}
What version of WordPress are you using? I believe some other plugin is conflicting and throwing this error returned along with the rating result. The line in plugin.php tries to remove a menu page. Do you have any functionality which does this?