You can integrate and support all your Amazon Seller accounts into one PRO account!
In order to link separate Amazon Seller accounts, click on the Connections tab from your left navigation. On this page you will see a list of your currently connected marketplaces. To add a new marketplace, click the "Add Marketplace" button to start the process of adding a new marketplace.
*Please keep in mind that PRO plans are based on annual sales for all active connected marketplaces. You are not charged per additional marketplace, but their annual sales will be included in the grand total to make sure the account is on the correct plan.