Item was not added/updated, Product Type is not valid or empty.

The error may occur if the Product Type of an item has been updated on Amazon.

You can resolve the issue in two simple steps:

1.  Update the marketplaces you're selling the item. Go to Amazon>Configurations>Marketplaces and click Update.M1:
   
   M2:
   
2. Edit the description policy (Amazon>Configurations>Policies or Amazon>M2E Pro Listings>Listings grid>Settings View Mode) and select an appropriate Product Type.