How to access the REST API

I have followed the following instructions as stated on the documentation website:

https://developer.imis.com/docs/accessing-the-rest-api

Log in to iMIS.
Retrieve the verification token from the page. The token is stored in a hidden field with the element ID RequestVerificationToken.
Compose an HTTP Web Request.
Add the token to your request header as RequestVerificationToken.
Complete the request.

I just get a 401 error. Please can you tell me the actual steps for accessing the API. I have noticed when i refresh the Imis page then the RequestVerificationToken changes every time anyway. I have no idea how this should work.

I am using Postman to make the request to https://{{site_url}}/api/Party with a header of RequestVerificationToken: {token_copied_from_hidden_field}