If a shipping confirmation has not been reported to Zalando, open the menu Data > Log:

Use the following filters:

• Integration: Plenty\Modules\Zalando\Orders\Procedures\OrderShippingProcedure
• Identifier: Zalando
• Level: error

If necessary, you can also filter by the Order ID/External Order ID:

• Reference type: orderId / externalOrderId
• Reference value: your Order ID / your external Order ID

An example: