Most complex crdts are built on top of the simple crdt of a grow only set. Ie, what we actually synchronise over the network is a big bag of commits / operations / something such that the network protocol makes sure everyone ends up with all of the operations known to any peer. Then the crdt takes that big set and produces some sort of sensible projection from it.

> You just have to make sure not to record the same transaction more than once

So this should be pretty easy. Have a grow only set of transactions. Give each one a globally unique ID at the point of creation. Order by date and do bookkeeping. One thing you can’t guarantee is that the balance is always positive. But otherwise - yeah.