TradeDirect master shipment cannot be closed error.

[JayRahnama]

Hi,

I'm in the process of implementing UPS Trade Direct and wanted to outline the steps I followed:

A master shipment was created successfully. This returned a USI, transId, and transactionSrc, which I stored.

Throughout the day, incoming shipments were assigned to this master shipment using the USI and were created as child shipments.

Up to this point, everything worked as expected — I was able to retrieve labels and files for all SMALLPACKAGE shipments.

However, when I attempted to close out the master shipment, I received the following response:

{"response":{"errors":[{"code":"400105","message":"Master Shipment can't be Closed"}]}}

Do you have any insight into why the master shipment might not be closing successfully? Are there any specific requirements (e.g., minimum number of packages, timing, or shipment status) that need to be met before a master can be closed?