Go to the Configuration Page, and Expand Marketplace Settings.
Click on the Add Additional Marketplace button.
Select your preferred Amazon Marketplace from the Amazon Marketplace drop-down menu, post-selection you will see this "Find the link for the app in Amazon Marketplace Appstore (You should be logged in Amazon seller central)" text, above the Amazon Marketplace drop-down menu, here click on the link. Note: Please make sure to log in to the corresponding Amazon Seller Central account, before clicking the link.
Click on the Authorize Now button.
Follow the onscreen instructions as per these below-displayed images, and COPY the Seller ID and MWS Auth Token.
PASTE the above-copied Seller ID, MWS Auth Token inside our app, and hit the Authenticate & Save button.
Post clicking the Authenticate & Save button, you will see a Success message, else you need to COPY the correct Seller ID and MWS Auth Token from step 5, and enter in step 6.
In case, you have any questions OR suggestions, feel free to reach out to us at email@example.com.