For every call made to all APIs, the following headers should be present:

Accept : application/json
Content-Type : application/json

Also, the access token generated during authentication should be present in your headers in the pattern below. Let's assume you have an access token,eyFjhjtywuiTYgvkkhhuuJKKllllm, the header should look this way:

Authorization : Bearer eyFjhjtywuiTYgvkkhhuuJKKllllm