This was originally optional, but it is possible that it has been changed to be mandatory. I will check and confirm.
I have read the DHL regulations for shipping to a postfiliae and it is handled the same way as shipping to a packstation.
Is is explained here: https://www.dhl.de/en/privatkunden/pakete-empfangen/an-einem-abholort-empfangen/filiale-empfang.html
This is the response I received from DHL Support:
postfiliale:
Post Nummer of the receiver or receiver e-mail-adress
The postnumber must be 8 or 10 digits long.
packstation:
Post Nummer of the receiver, if not set receiver e-mail and/or mobilephone number needs to be set. The postnumber must be 8 or 10 digits long. When sending to a packstation with “DHL Paket” (V01PAK), the postnumber must always be entered.
Yes but that’s the issue! As already said we are getting an error message for postfiliale if no postnummer is set and even if an email address is set:
“Could not create label – Postnummer oder E-Mail-Adresse muss gesetzt sein.”
As the postnummer field in the checkout is optional customers forget to add their postnummer and we are not able to create the label without asking them. Therefore, I had asked if there is a possibility to display the postnummer field also as a mandatory field just as it is already with the packstation! It would be nice if you would just answer my question and not tell me again what I already know!
Can you confirm if you are sending over the email via this setting – https://www.dropbox.com/s/fg2cx7ug7qv34yk/screenshot%202021-01-29%20at%2014.27.33.png?dl=0. It might be why you get this error.