If you receive the "Prep Information Needed" error, you will need to assign a Prep Type to your MSKU. This must be done directly in Seller Central.
Prep Type: Specific packaging or preparation methods are required to ensure that products are ready for safe storage and shipping through Amazon's fulfillment centers. Each product may require different types of preparation depending on its nature, size, and material to comply with Amazon's guidelines for packaging and labeling. Some examples of Prep Type include poly bagging, bubble wrap, and taping.
In Seller Central, click the hamburger menu (three stacked lines) in the upper left.
Select Inventory, then Shipments.
Select Shipments > Send to Amazon at the top of the page.
Start a new Send to Amazon workflow by clicking Start New in the upper right corner.
Search for the MSKU you need to update the prep information for.
Click on the Prep and labeling details needed link.
A pop-up will open. Click Choose prep category and choose from the available options.
a. Depending on the prep category you choose, you may need to make additional selections.
Once you've finished, click Save.
Now that the prep type is saved, you can navigate back to InventoryLab and continue listing.