Hey there! First of all, so sorry your question hasn't yet had a response from another seller, or from us. We were pleasantly surprised by all the posts when the community went live early last month, so I apologize this slipped through the cracks. We've added some more people to our team in the last week, so I hope you'll give it another shot in the future!

With regards to your question - we only require a 5 digit zip code, and as long as it's accurate, the transaction should go through. In order to protect both buyers and sellers from fraudulent transactions we do require all card information to be 100% accurate for a manually keyed in payment to be successful.

Assuming you've triple-checked the zip code's accuracy, I'd recommend having your customer check with their bank to make sure the zip code the bank has on file is accurate. Sometimes folks move, and forget to update their zip codes and that can cause trouble. Also, it could be that the card the customer is trying to use maybe has some strange stipulation for zip codes associated with it so it would be worth them asking their bank about that too. 

Let me know how it goes for you!