PLEASE NOTE: eBay errors are common. If your item is receiving an eBay Error when trying to list, you can learn more by clicking "Read error message" to see what eBay is asking from your listing.
When you get the postal code error, you need to update your JOELISTER_SHIPPING_PROFILE eBay business profile on eBay.
Your JOELISTER_SHIPPING_PROFILE should be set to "Flat:..." in the setting shown in the screenshot below. If you have set to "Calculated," then eBay will not know where your FBA inventory is located, and the listings will fail. Once the setting is set to "Flat," then you should be able to list normally.
If you need more guidance on how to manually edit eBay Business Policy Profiles, click here.