Checkout postal code validation uses metafields in Shopify to check the customer postal code in the checkout and ensure the correct rate displays to the customer.

The metafields contain your location information, the postal codes in your settings and your rate configurations. If your set up is too complex, the metafield data can exceed the maximum, and cause rate issues.

Too many metafields can cause:

To fix these rate issues you can reduce the number of metafields.

You can reduce the number of metafields by disabling the Checkout postal code validation setting, or by simplifying your postal code and rates set up.

Your customers postal codes will not be validated at checkout, and your rates should work as expected.

You can simplify your set up by reducing the number of locations you have, the number of postal codes in your delivery validation fields, or the number of rates you have.

If you have any locations with pickup or delivery disabled, review if you can combine any locations into one.

If you are using exact matching postal codes, review if you are able to simplify the set up and use partial matching.

Check for any redundant rates and remove them. If you use location specific rates, check if any locations can share the same default rates.