Granting access to the Selling Partner API will allow M19 to fetch your Sales data from your Seller Central Account.
API access is only available for seller accounts.
This access is essential to create product groups, download, and update automatically the account's catalog and "all sales (organic and sponsored sales)" KPI.
Click the “Grant API Access” button, which will lead you to your Seller Central account.
Log in to Seller Central
If you are not logged in yet, you will be prompted to log in to your Seller Central account. Log in with an admin profile.
Make sure the profile has the following authorization: Performance section -> View & Edit for Marketplace Appstore. If not, you can provide it by going to the settings in your seller central -> User permissions -> Manage permissions (for the concerned user) as depicted below -