It would be very useful to be able to link transactions that are related together so that you can quickly access them from other transactions.
I’m thinking especially that it would be useful to link refunds to the transactions that are being refunded. Obviously, this might not be possible to do automatically, but doing it manually through a system similar to the tagging and description systems would be massively useful to me.
I would love this, as I often have to ‘repay’ myself for an expense from a lot or another account. Linking the transactions would be 
!
I hadn’t even thought about that particular use-case, but that definitely is useful to me too.
I’d been thinking about how McDonald’s accidentally double-charged me yesterday and refunded it today, and for card verification charges that don’t get reversed transparently and are instead refunded.
But another useful one is where a friend gave me some money to pick up lunch for him - linking those transactions together would be useful as well. That was a payment in (money from friend), payment out on debit card (to pay for lunch), and a payment out in the app (change for friend), which would be helpful to link together in some way.
Firstly, apologies for creating duplicate threads on this topic. Please ignore my own thread on this subject and, ideally, flag it so it gets deleted.
I created this account just to make this suggestion, only to find it exists! Still, I’ll elaborate and hopefully the original suggestion will get some more attention.
My thought is essentially threading transactions, as Gmail does related emails. Perhaps showing a small line of text under a transaction that shows that there’s a related transaction. Tapping on it could show this, below the usual transaction information.
For my purposes, I like to keep an eye on money transfers. I’ve sent myself some money abroad to change into Euros and then sent it back. I’d like the “refund”/return transaction to be linked, so I can easily see the difference. The accounts would of course be different and the transactions days apart, so perhaps it could be linked based on a custom reference entered by myself in both transactions and rules could auto match and link them.
Another example would be lending money to a friend and being able to later see when they repaid it.
Another might be a for a stockbroking company such as Freetrade; linking the deposit amount to the amount received - plus perhaps any ticker symbols left in the reference/notes section - when one cashes out after a sale, as it were.
I think there are many potential use cases for this.
Someone said on the other thread (sorry again about duplicating things!) search could be used. It could. One could also indeed tap on a transaction to see how many payments have been received or made to that payee. However, you can’t search by the amount of a transaction and the payee/accounts won’t always be the same. My hope is that Monzo smarts and some machine learning could hopefully find patterns in transactions that would save us humans some time in trying to hunt down that related transaction.