Since we need to use HTTP post for note creation, it is necessary to get a CSRF token first. Use the following settings in Chrome extension Postman to fetch a CSRF token:

Then assemble a new HTTP post request with following settings, in http payload tab, choose option “raw” with format JSON, and paste the following json string containing Opportunity header guid and the note content you would like to create, click send button:

You should see the successful creation response: