I have added Schema Code (Json Ld) for organisation with ratings, there's no error in the Structured data testing tool + it shows correctly in the preview result. But even then the Ratings are not being shown on Google Search.
The first point I would say is that whether the ratings show in SERP results or not very much depends on whether search engines have picked up the schema yet.It takes quite some time. Have you checked Search Console to see if Google is picking this up in the structured data report? Secondly, even if Google is acknowledging the mark up, it may not show the rich snippet at all or for some time. If you have it implemented correctly, it can be a waiting game.