Zonmaster, and other services like us, require something called an MWS Auth Token. MWS stands for Marketplace Web Services and is a feature enabled on Pro-Seller accounts on Amazon.
To tell if you are a pro-seller go to the account information page in the seller central of your market (eg for Amazon.com you can go here: https://sellercentral.amazon.com/hz/sc/account-information)
Under 'Your Services' you will see something like this:
Indicating you are a Professional seller on Amazon.ca (in this case).
