I am trying to move documents from one library to another using SPD workflow there trying to use some Rest API but am not getting it. can any one help?
You could create a custom rest API that receive identifier about the document which you want to move (its ID for example), and the destination library name/id/whatever identifier.
For example, you create a rest API on:
The next thing to do is to perform the move operations in your rest API code. You could refer to the sample code of moving document from one to another library here.
You could throw some string / status code / whatever as the response of the rest API, to indicate whether the rest API call is successful / failed, and store it as a variable on the SharePoint Designer.