Last week I was working with SharePoint rest API. In some terms, I needed to do some complicated query in a SP list. To do these queries I prefer CAML. But to use CAML with SharePoint rest API, I have been banging my head against the wall for a couple of days as I was stacked with errors. At last I got the solution I wanted.
Using the code
So, what I missed, is the first condition of using CAML with rest request. That is, it always has to be a POST request. The request header is as same as the other normal post request for SharePoint Rest API.

The REST endpoint for using caml query is

The complete code with the rest call is given bellow:

The CAML Query has to be used in between this <View><Query>…CAML Query…</Query></View> tag. The query with the way to call the function is given below:

Points of Interest
The CAML query can also be used in query string of the rest request. But it makes the URL unnecessarily complicated. If anyone knows of any better approach, please let me know in the comments below and I will update my article.