You need two tokens to use the API - the api token in the plugin section ('admin/configure-plugin/pluginAPI') = the api token - this is used to request pages and page details. The other is the authenticated user token ('admin/edit-user/admin') / Security tab for Authentication token.
To grab a page be sure you are putting your api token in the get request. The token is put in the Params section in Postman
To create a page be sure you are putting your api token and authentication token in the in the post request. The token is put in the Body section in Postman as form data