A quick google and this seems to be the mastercard fee.
Visa & Mastercard charge a fee in addition to your bank. Possibly the transaction was at a weekend and a blended rate was therefore not possible.
You can check calculations here -
Find the foreign currency exchange rates used for cross border transactions for all major world currencies with Mastercard’s online currency converter tool.
From Bonkers
Use N26 or Revolut
Using N26 or Revolut is the simplest way to avoid foreign exchange fees and if you use either of these banks then you won’t need to take on board any of the other advice in this article.
Both N26 and Revolut have shaken up the banking sector since their launch a few years back. They both offer a host of novel services, which you can read about in more depth here. But a key benefit of these banks is their lack of foreign exchange fees.
As you can see from the tables above, all the traditional banks will charge you a 1.75% to 3% foreign exchange or ‘processing fee’ for purchases made with your debit card outside the Eurozone, which can really add up.
But N26 will charge you nothing while Revolut will charge you nothing on all major currencies up to a limit of €1,000 a month - after that there’s a small 0.5% fee.
What’s more, when converting your spend back into euro, N26 applies the Mastercard exchange rate at all times while Revolut applies the Interbank exchange rate with a 0.5% mark-up at weekends on major currencies and a 1% mark-up on less common currencies. Both these rates are likely to be better than the rate you’d get with one of the main banks.