authorization token at the 'Authorization' HTTP header.

Hi

I am following the following quick start tutorial on how to make a call to the Sage API https://developer.sage.com/api/accounting/quick_start_guide/create-your-first-request/. through postman. I follow it step by step however the error I am getting from Postman is the following:

{
"error": "Authorization missing. Please, add an authorization token at the 'Authorization' HTTP header."
}

Thanks