Is the Print Products Store set to the correct country?
Where did you check these?
- The Print Products Store needs to be set to your country in the Photos > Preferences > General.
- The Store account details need to be checked in the Photos > Print Products Store menu.
Have you entered them again? Occasionally invisible characters can be interfering. So enter the details again and do not just check.
It also might be the address format of your Contacts card.
To get the formatting right, make sure the format of your address on your Contacts Card is set to your country.
If the format of your Contacts card is not set to your country, you may be seeing the warning about the invalid ZIP code or wrong country:
Open your Contact card, click "Edit". Ctrl-Click the label (Home or Work) for your address on the card and select "Change Address format". Set it to your country.

Photos will also get the country wrong, if you insert spaces into the zip code.
Also check the System Preferences. The TimeZone in System Preferences > Date and Time needs to be set to your country. The System preferences > Language and Region need to be set to your country.