First you need to know what went wrong.
If the client didn't provide clear enough instructions to their bank, they need to take it up with their bank. Meanwhile, I would say they still owe you the amount unpaid... though you may want to eat that difference this time, if it's an important sale.
BUT: If you provided them with the instructions they provided to their bank, I'd say that's your fault and they shouldn't have to pay to fix it. Work with your own bank to find out how to prevent this from happening in the future.
My perception is that international funds transfer is a problem waiting to occur, since there are a lot of restrictions and opportunities to make mistakes. Verify EVERYTHING before sending the money. In fact, you may want to send a small amount first, to confirm that the right processing happens and correct any errors before committing a large amount.