Have you seen this? Email Receipts in Monzo
It allows you to forward emails from amazon and associate the receipts with monzo transactions.
I think paying in cheques by photo shouldn’t be a chargeable service, monzo are already saving by not having to have high street banks where you could do this with another competitor. I wouldn’t be very happy moving from Barclays where I can deposit in branch to having to pay £1 to take a photograph.