Welcome to the community!
The terms & conditions for your Monzo card explain when you will & won’t be liable if your card is used after you have lost it -
At the moment, these terms cover the scenario that you’ve described:
You may not be liable for any use of the card, card number, PIN or mobile application by another person who does not have your permission to use it or if it is lost, stolen or destroyed, unless:
you agreed to that person having your card, card number, PIN or mobile application credentials, or through gross negligence or carelessness, failed to comply with condition 9.1, in which case you may be liable for any use that occurs before you tell us in accordance with these terms and conditions, or
you acted fraudulently then, to the extent permitted by law, you may be liable for misuse of the card, card number, PIN or mobile application.
you may only be liable to a maximum of £50 resulting from transactions arising from the use of a lost or stolen card or from the misappropriation of the payment instrument where the cardholder has failed to keep security features of the card safe. The £50 liability limit is applicable to each instance of loss, theft or misappropriation and not each transaction.
I don’t work for Monzo but the implication is that they will be liable for these transactions so Monzo will reimburse you for them.
Bear in mind that the terms also state that:
If your card is lost or stolen or someone else finds out the PIN or if you think your card, card number or PIN may be misused, you must;
without undue delay, pause the card within your Monzo mobile application. You can also permanently cancel the card via the mobile application. If you do not have access to the mobile application, call us without undue delay on 0800 8021 456 (we have a 24 hour service) so that we can stop your card and PIN;
stop using the card, card number or PIN immediately. If you find the card after you have temporarily paused it, you can re-enable it via the app and continue using it. If you find the card after you have reported it permanently lost, stolen or misused, please cut it up and dispose of it.
As for -
This will depend on the type of transaction & circumstances so I don’t think it’s possible to provide a comprehensive answer to that question.