Problem

When creating postage stamps (Internetmarken), this error occurs:


 Undefined array key "shipping_product"

Cause

Use the command "bin/magento module:status" to check if all modules are enabled whose name starts with

  • Dhl
  • DeutschePost
  • Netresearch


Most likely, the module "Netresearch_ShippingUI" is not enabled.

Solution

Enable the module "Netresearch_ShippingUI".