What can I do if I'm unable to process my DTV Visa payment on the Washington DC consulate website?

Sorry you're stuck on that step, it's frustrating when a portal won't take payment. One thing worth trying is calling your card issuer to allow international online transactions and any extra authentication, then retrying in a fresh browser window. If the consulate still doesn't answer, it may be worth asking in this group who succeeded recently.

Sawadee, yes many people see same payment error on DC website these days. System often blocks if address or card is not US or if amount is high. Try use US debit card with US billing zip, clear cache and use Chrome, and try morning time Bangkok time when server is less busy.

If phone not answering that is normal for DC, they reply slow. Try email again with subject payment failed plus your passport number, and include screenshot. Some people pay via same account after two days and it works.

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Use search including Embassy name, you are asking questions that has been answered numerous times.

Been a while, but when I had that problem I changed to Google Pay with the same credit card and it worked. I think they still take GPay

Try a different card. I had two that wouldn't work (same bank) but another bank's card went through fine. Something in the way it was transmitted to my bank card made them reject it. Maybe the way the address/zip code was input. When I contacted my bank they checked and just said it was rejected because the information didn't match.

Visa or master card, credit or debit, it says and requires online payment only. While you were trying to pay, there might have been a system error or network traffic overload. Not a bad idea to try again during the next working days.

This has happened before as many posts in the thread show, frequent problem especially on weekends. Trying again later is often best, the system usually sorts itself out after a few hrs.