by Edwin Torn Broers.
Hi Charan,
Just tried this one on our 3.1 system (with postman) to get information on courseid 12.
https://<your-server>/webservice/rest/server.php?wstoken=<your-token>&wsfunction=core_course_get_courses&moodlewsrestformat=json&options[ids][0]=12
However this does not answer your question. This API call is probably not what you are looking for because it does not support categoryid as a selection parameter. I took a short peek at other calls and I'm not sure if what you are looking for is available.
Regards,
Edwin