Has anyone had any luck in trying to use a US credit card for this? The India OTAs have enough 1 star reviews to go to the moon and back several times, so not too keen on that option.

I called Chase, the CSR apologized but said they don't see any kind of transaction on their end. He did say it was a known issue with many Indian companies and affecting Visa, MC, and Amex. He suggested I call Indigo and complain to them...

I do have an Amex, but all the travel protections only work for round trips and I'm booking a one way.

Not sure which Indian OTA you’re using but sites like Makemytrip, Yatra etc. are absolutely as good as any other OTA. Plus you anyways will have your CC protection. Otherwise, you can use Expedia or any other OTA to book 6E flights.

A few weeks ago I paid Indigo using my US Amex Plat, went thru without a hitch using the safekey validation.

Does Indigo have flights show up on Priceline.com? Priceline.com flight bookings for domestic Indian flights seem to work just fine with Chase cards too — whether it be at least Air India, Vistara, Spice, Go.

No go on Makemytrip, they require a PIN (they actually charged the card, bank approved it, then Makemytrip sent it back... umm wow?). Yatra says transaction declined by bank, not true of course, Chase can't see anything even making it to there end.

Expedia does not show Indigo. I ended up going with Booking even though they are really just a passthrough on flights for Gotogate.

While I have had minor issues conducting international transactions over the past 20 years, this is the first time multiple entities in a country simply refused money that was offered to them.

You can absolutely buy 6E tickets on Expedia.

There are many many countries that have blocked or have issues with foreign credit cards. More so if they're the less secure variety. I've faced plenty of issues the world over. Iceland - probably the most CC savvy nation didn't allow my Citi Prestige card in-person anywhere except at petrol stations. Many parts of Latin America will not allow you to buy anything online - not even a pizza - with a foreign card.

India should absolutely ease up on using foreign cards to buy airlines tickets online, after all, using foreign cards online in India is allowed pretty much everywhere else. They introduced this block due to a massive fraud that occurred many many years ago. It's high time they lifted this ban and got better processes in place.

^ does not seem 6E is on Expedia from my search.

I ended up using AMEX on my end

Indigo and foreign credit cards - the problem is not that you can't buy a ticket, you can often buy them on the OTA's like Expedia. But then you have no extras (baggage, seating, ...) and you can't buy those from the OTA's. So you end up paying more for those things at the airport.
A workaround that I found is to order these on the indigo web site, the payment (with a foreign CC) will fail, but they will hold the booking for the extras until you fly.
At the airport, go to the Indigo booking office, pay the amount showing as due in your reservation (foreign credit cards accepted), and then you are good to go.
Worked for me in DEL and Leh

Is anyone having trouble signing up for Indigo account? This is the error I get:


https://cimg4.ibsrv.net/gimg/www.fly...9c19677e46.png

Last week I tried to book an internal flight Bombay-Ahmedabad on Indigo and Vistara websites using my US issued visa card but the payments did not go through. I tried my UK issued cards and the same problem arose. I then twitted the airlines and they confirmed that their IT system accepts only Indian issued credit cards.

In the end, I booked the flights through Expedia.com without any hassles including free seat selection and meals at the time of booking.

Well RBI's foreign card diktat appears to have gone into over-drive mode preventing most India based airlines to decline EU issued cards too. My German Mastercard which always used to work on 6E website no longer works as payment gets declined.
While India based OTA's such as Yatra, MMT are no longer accessable in EU due to some crazy GDPR rules, 6E tickets sold via Expedia, etc. are non-refundable (no flex-fare package offered which also consisted some basic free seat selection & a light-meal) is now all gone.
Beware these OTA's also add their own fee on top of carriers for changes/cxl, etc.

Found a good solution
 

Problem here is that
(a)direct bookings with Indian domestic carriers with a US credit card is impossible--they haven't figured out to incorporate legally required verification steps (either sending a one time password message or linking to the Verified by Visa type options US credit card banks use)
(b) bookings with US credit cards are possible using International OTAs (e.g. Expedia) but they don't offer critical options available on the airlines' websites (different levels of economy fares, seat assignments, other ancillary services)

The domestic Indian carriers think the use of international cards is possible (and if you call/email them they will insist there is no problem) but have never bothered to test whether customers can actually buy tickets.
Unclear whether the big OTAs just don't care or are actually trying to rip off foreign tourists. I found two that demand outrageous seat assignment fees (US$17) versus the R300-400 the airlines charged, and even tried to impose them when seat assignments were included in a "Flexi" fare. Some sites (including Travelocity) offered nothing but the stripped down basic economy fare and didn't tell you there were other options and you might get stuck with very high charges when you got to the airport. The OTAs have obviously figured out how to sell European and US LCCs so there are no technical obstacles here.

Solution I found was to use the Indian OTA Make My Trip. When you sign up and set up a profile they will send a one time password verification which covers the Indian government's two-step verification requirement. Could use whatever US card I wanted, and they provided full access to each airline's actual fare offerings (Basic economy, flexi, premium, etc) and each airline's seat maps and meal and baggage options. Make My Trip has separate "US" and "Indian" booking sites. You may need to use the Indian site

Sorry to burst your bubble, but Amex safekey works like a charm for the US Amex. The 'verified by visa' is called up by the website, but declined by Chase credit cards (or rather waived thru without verification) and thats where the process fails. The US credits that fail the Indian RBI standards also fail in the EU with their PSD2 standard. Since the online payments outside of the US is not a big topic for US banks they have not adjusted their 2FA verification systems.

problem was us based visa/mastercard
 

Correct but all of the earlier commenters voicing frustrations didn't have amex or wanted to use their preferred visa/mastercards

I have faced enough problems with Make my Trip in the past & have decided to stay away from them permanently.

Going through the airlines own website will be the better option 99.9% of the time.