I have tried printing a Deutsche Post shipping label and am seeing an error returned:

items[0].contents[0].contentPieceDescription: size must be between 1 and 33


Unless there is a separate item extended property for customs description, the inventory item's title will be submitted as the parcel's content description. The above error means that the title does not exist, or is exceeding 33 characters, which can be checked and edited in My Inventory section.

Alternatively, a shorter description for customs documents can be assigned to the item's extended property, which can then be mapped to CommodityDescription field in > Shipping > Properties.

Related articles:

Shipping - HS Tariff Code and Country of Origin
Shipping - Adding shipping details to items