SPOnline Search REST API POST requestNovember 27, 2016
There is one thing about Sharepoint. It doesn't let you pass even if there is a slight formatting error in your request. And, most of the time error is not so appropriate or no error.
I faced the same situation when i tried to compose a POST request for SPOnline Search REST API. The query text was quite complex as I was trying to retrieve search results based on a managed property which is in turn is generated from managed metadata column. The key here is not introduce + symbol in place of space as we would generally do in GET request.