Make sure you have a Professional Amazon Seller account. It is required to use ScanLister and any other 3rd party software program.
If you are still unable to connect ScanLister to your Amazon account, please try the following:
1) Copy and Paste the Seller ID and Auth Token to insure accuracy
2) Make sure there are no spaces in front or behind the characters.
3) Include the "amzn.mws." in the auth code.
4) Make sure you use the Seller ID (Not the Marketplace ID).