I had to buy a ticket with Swiss Air and it asked me to either pay with Credit card (Visa, Mastercard, etc) or with Debit card (Maestro, etc). I selected credit card because the Monzo card says Mastercard on it but it told me it was the wrong type of card. So I tried debit card with Maestro and it said it was not a Maestro card.
So I could not actually pay with my Monzo card 
In the end I used a back-up credit card I have.
MasterCard debit card rather than credit is the option to use
Iāve looked, that isnāt an option.
I think this is an acceptance issue of some kind, and can only be answered by someone from Monzo who can offer some insight of whatās going on on a technical level?
As for the OP, @RelaxWithDax - I think your best port of call might be to report this using the in app chat and see if they can investigate and get you an answer quicker that way.
Looks like itās been an issue for a few years:
Itās probably safer to buy things like airline tickets on credit card because of the extra refund protection you get.
Iāll flag this up with acceptance to take a look at! 
Sure, but I donāt have a local credit card yet and it costs me to use my overseas card.
Cold comfort, but this looks like a problem with the retailer rather than Monzo, to be honest. If they donāt take MasterCard debit cards then theyāre ruling out a lot of the market. Seems like a weird decision on their partā¦
Agreed. This isnāt Monzo. It would affect anyone with a Mastercard debit card.
Itās Swiss beingā¦ well, annoying.
Iām currently working in the Netherlands and have encountered a number of places that donāt accept MasterCard debit or credit. Iāve just been to a major supermarket and they wonāt take MasterCard, Visa or Amex. They say Maestro donāt charge a transaction fee, so itās all theyāll accept.
I donāt consider it a Monzo issue, but just a quirk of the country not liking MasterCard.
Iām amazed by this. How can they get away with this in this day and age 
Your probably used to thinking you can use card everywhere but the reality is different when you include the rest of the world.
Oh no, that wasnāt my trail of thought at all 
. In my mind Netherlands and Switzerland are very much like the UK and are geographically in mainland Europe, I would have presumed theyād be very much similar to the UK when it comes to card acceptance. Maybe I thought wrong 
It varies widely. Germany for example as far as Iām aware basically did away with cheques but cheques are still widely used in places like the US, UK, and France. Chip and pin has all but taken over in the UK but not in the US. And the US dollar is for all intent the universal currency, not debit card or credit or anything else but good old USD.
We do tend to live in a little bit of a bubble , but most places do.
I know this might not be of too much help, but as Swiss is a member of Star Alliance if you really wanted to use your Monzo Card you could purchase the ticket for the same flight via another star alliance partner like Lufthansa or Austrian.
As others have said, this isnāt a Monzo-specific issue. The same applies at Costco fuel stations - they accept Amex credit cards and Visa or Maestro debit cards (no debit Mastercard acceptance). Very annoying!
The ticket has to cost Ā£100 or more for that to apply.
Because in some parts of Europe Maestro and VPay (Eurozone only I think) are the dominant electronic payment providers. Theyāre an order of magnitude cheaper than Mastercard or Visa for merchants so outside of tourist areas thereās no interest in supporting the Visa and Mastercard. Same reason many merchants in the UK donāt support Amex - the fees are higher than Visa and Mastercard.
Costco fuel take any debit cards and amex, used my monzo card there plenty.
Really? Iāve definitely had a debit Mastercard refused and their signage specifically has Maestro rather than MasterCard. Iāll try again!