'Insufficient inventory capacity' error when trying to add items to a shipment. What does it mean?

Q: I am getting the following error when I try to add an item to a shipment / when I try to register or send a shipment:

UpdateInboundShipment response: ERROR_CODE: InvalidRequestException.
ERROR_MESSAGE: This operation may be partially successful, Please check the shipment.
Reason: Insufficient inventory capacity for the operation..

A: This error message is provided by Amazon. You may have an inventory storage limit. Inventory storage limits generally apply to new FBA sellers and existing FBA sellers with slower-turning inventory.

If your Amazon FBA account is configured for Unlimited storage then this error can also show up if one of the items in the Shipment Preview has an ASIN-level capacity restriction.

Please contact Amazon Support to find out if this issue is happening because you have reached your storage limit or because the item you are trying to add to a shipment has capacity restrictions.

Seeing such an error message would indicate that allocated storage space at Amazon warehouses is used up or that you have exceeded your shipment limit. Go to File > Preferences > FBA Settings and check that the "Maximum items in shipment" option isn't set to a number that's lower than how many items you want to add to a shipment. 

This can also refer either to your own storage limit for a certain item category or to the fact that for the time being there isn't enough storage space available. There is a limit imposed by Amazon when it comes to how many items you can store at any given point to sell via FBA and reaching that limit would trigger this error.

Check your available storage on Seller Central and if you haven't reached your limit to try again later. If that doesn't help please contact Amazon support.