This article outlines an error donors see when using the Donation Plugin.
"An embedded page at xyz.kindful.com says "Your Zip/Postcode is incomplete."
What does this mean?
When a donor is completing the donation widget form, you have the option to collect the address on the donation form as a way to create more complete contact profiles with these online donations.
In the top part of the plugin where you enter in the Credit Card details, a ZIP (code) is required. This is to the right of the CVV entry box. This postcode is meant for billing purposes as a part of the verification required by the gateways. This is because a billing address can vary from a postal address.
Then, as you move through the donation flow, a mailing address can be entered. This mailing postal code can be different than that of the billing postal code.