You can view your 14 digit Amazon Merchant ID (also known as Merchant Token) by clicking your name in the upper right-hand corner and selecting My Account from the dropdown menu.
Next, scroll to the Amazon Account Binding section.
If InventoryLab's authorization to your Amazon account expires, you can renew it by clicking Rebind.
You will then be taken through a short binding process with your Seller Central account which, in the end, will put you back into InventoryLab.
Once done, please allow 24 hours for any missing data to sync to your account.