What did “pay in your currency” cost?
Dynamic currency conversion (DCC) lets the terminal or ATM convert at its own rate. Enter the amount on the bill and what it offered in your currency: the difference to the ECB reference rate is the hidden markup.
The ECB reference rate for this pair is not available right now.
About DCC
Should I pay in local currency or my home currency?
In local currency, almost always. With DCC the merchant's payment provider picks the rate and keeps the margin; your card's own conversion is usually closer to the reference rate.
Is DCC allowed?
Yes, but in the EU the terminal has to show you the conversion cost before you agree, and you may decline it. Pressing the local-currency option declines it.
Where does the reference rate come from?
From the European Central Bank's daily euro reference rates. Cross rates (for example GBP to THB) are worked out through the euro.