Bought a refundable ticket that apparently was billed into a EUR, most likely based on the country of origin, despite using a US credit card. Cancelled the ticket, and was apparently issued a refund in EUR. The original charge shows up on my CC in USD for a higher amount than the credit shows up in USD. Presumably, I lost some money based on FX rate fluctuations. Do I have any recourse with either Amex or the airline, or am I SOL?

The refund will post to the same currency as the original charge was charged. It doesn't make a difference that you have a US issued card.

It indeed did. The issue is that I lost some money, presumably because N euros was worth more $$ the day the charge posted than the day the refund posted. My question is whether that is simply a risk one bears when buying a refundable ticket that gets charged in a foreign currency, or whether I have any recourse.

No recourse. Sometimes this works to your benefit and other times it doesn't.

Not at this point. How is this different from buying something in a Paris store on a credit card for 50 euros, having that billed to your credit card at the then-current exchange rate, and returning it a week later, having a credit based on the new exchange rate? Why would you expect anything different to happen?

You could have also made some money. If that had happened, how would you feel if the credit card had come after you for your ill-gotten gains?

The solution, if you think you might refund something and you think the exchange rate will work against you if that happens, is to have the cost charged in USD. That may incur other costs. Take your pick.

(FWIW, that happened to me once with a refundable ticket purchase in Australian dollars. I bought it to get into a lounge during an FT OzFest event and refunded it soon after. I figured it was the luck of the draw. That, plus the difference amounted to about the cost of two flat whites. Not worth getting upset about.)

If you don't want to be exposed to currency risk buy the ticket in your own currency. You will of course be subject to the carrier's exchange rate when you do this, which may be better or worse than your CC company. Since you chose to purchase it in EUR, the carrier was right to refund you the exact amount in EUR that it charged. You have no recourse.

The credit card cartels will get you any way they can. They do foreign exchange at bank rates, i.e. the selling rate is several points higher than the buying rate. This is why you see the discrepancy. Also, depending on the timing of the purchase and refunds, currency fluctuations come into play - might be more, might be less. Finally, there is a hidden commission of ~2.5% on foreign currency transactions processed on the major credit cards.

Frankly, the whole thing is far more of a scam than airline FF programs, but the cartels are clever enough to hide it better than the airlines do.

I had a similar experience a couple of years back buying 4 J seats for the family to travel from Japan to Australia with Qantas.

I booked and paid on the Japanese site in yen using my Australian credit card. The charge initially could be seen to have been applied to my card (available balanced decreased)...but then disappeared and 6 weeks later finally billed at the Exchange rate for THAT time (not time of booking). Difference was 1500 AUD due to a significant FX fluctuation.

Complained to Qantas... they blamed bank/card provider. Complained to bank...they blamed Qantas. Got nowhere with it other than understand-but-nothing-we-can-do except allow you to refund with no charge
response by the local Qantas office.

In the end I left it but was a big learning to avoid big purchases on card in foreign currencies as you can't always control when the charge will hit and with what FX rate.

You have no recourse unfortunately. As far as the airline is concerned you paid a certain amount in Euros and that amount was refunded to you. That was your risk to bear.

Actually, some credit cards will credit you the difference if you just ask nicely.

And Amex is not one of them, in my opinion.

Have you verified whether this was due to change in FX rates over the time period or due to different buy/sell exchange rates by the card issuer?

If it's due to FX changes, I don't see how the card issuer can be liable for the FX risk. They don't make and money on the deal.

If it's due to different exchange rates, I would ask them to calculate the refund using the same metric (not the same rate, but the same type of rate on the different dates) and refund you the difference.

This happened to me recently with a hotel stay. They double charged me for a room in the foreign currency. When I pointed out the error they issued a refund but the refund was lower than what I was charged. The hotel made it right with bonus points.

No recourse. You knew it was charged in EUR when you bought the ticket. It's quite clear on the screen. Maybe you missed it but it was there.

There is a difference between the correction of an error and a simple refund. In the former, the merchant vendor ought to make the consumer's loss right, e.g., the consumer was double-charged and should not suffer a currency exchange loss because the merchane vendor made an error.

Here, OP simply purchased a product, chose to "return" it as he is permitted to and received a refund. He received that refund and chose to do all of this with a US$ CC payable in EUR. As a currency arbitrageur, he lost on this deal.

Either purchase in the card's "home" currency or only purchase in currencies which your crystal ball tells you will increase or at least remain stable.

You will find precious few threads on FT which start with, "I purchased in XXX and it went up, what do I do with the extra US$???"