For completeness - this has been solved. Details:
When using the REST API, you use your username and password, NOT the API Key.
API key-based authorization is not supported on Pulseway. The API key is only used for this API called the "Cloud API" and it is not used for RESTful API's.
As for the authentication on Postman, Authorization Type as "Basic Auth" and enter your Pulseway User Name and Password in Plain Text. The base64 encoding will be done automatically by the System.
