Why am I receiving the error message “The user is not authorized for this operation based on the provided...” when submitting a call to any of the webservices?

Make sure to check if your customer credentials have been implemented correctly in the call to the webservice. Required credentials are: Customer Code, Customer Number, API key, Barcode Type. These credentials need to match the customer credentials combination as shown in your MijnPostNL portal administrator account (My Account > Manage API).