I think it would be useful for the app to send through a push notification when the amount at the pay at pump updates.
For example I just spent £50 on fuel at Asda but it’s obviously only showing the £1. Now the only way I can see when it updates is by opening the app in the next few days and seeing if the balance has refreshed. It would be nice for a push notification to say something like ‘Just to note, your Asda fuel transaction has updated to £50’. I’m sure Monzo can word it much better! 
The same could even be done for transactions abroad where the amount may change due to the currency conversions. I’d quite like to see in the app the difference between the original and settling amount anyway.