1. In order for Seller Engine Plus to work, you will need to authorize it for access to Amazon's SP-API. This way the software can retrieve needed data from the Amazon API.
To authorize, go to File > Preferences > Amazon information, and click the Authorize Now button:
2. Clicking the Authorize Now button will take you to SellerCentral, you will be asked to log in if you're not already logged in through your browser. Review and accept the access request:
3. Complete the authorization process by following through the steps until you see a screen that says "You can now start using SellerEngine Plus."
To double-check that Seller Engine Plus is now able to retrieve data from Amazon make sure there's a green checkmark icon in the bottom-left corner of the SellerEngine Plus window: