Using with WP REST API (WP API) json_no_route error

After Installing this plugin I tried all three types of methods for getting json of related posts however got following error. [ { “code”: “json_no_route”, “message”: “No route was found matching the URL and request method” } ] Links tried: http://example.com/wp-json/posts/%post_id%/sirp_related/ http://example.com/wp-json/sirp_related/%post_id%/ http://example.com/wp-json/sirp_related/%post_id%/?filternum=5 Should I have to modify any other files? Which files? https://wordpress.org/plugins/wp-simple-related-posts/