Glossary
Combined transaction
A combined transaction bundles a digital euro payment with a funding step (reverse waterfall) or a defunding step (waterfall) in one operation.
Definition
Combined transaction
A combined transaction is what it sounds like: a payment and a liquidity movement travelling together as a single transaction rather than as two separate ones.
The two shapes
There are exactly two:
| Shape | What happens | Mechanism |
|---|---|---|
| Payment with funding | The payer does not hold enough digital euro, so money is pulled in from the linked account as part of the payment | Reverse waterfall |
| Payment with defunding | The payment would leave the payee above their holding limit, so the excess is pushed out to the linked account | Waterfall |
Why it is one transaction and not two
This is the part worth internalising. It would be possible to model "top up, then pay" as two independent operations. The scheme does not. The funding step and the payment are one combined transaction.
That matters because it removes a class of failure that would otherwise be unavoidable. If topping up and paying were separate, you would have to handle the case where the top-up succeeds and the payment then fails — leaving the user with a balance they did not ask for and a purchase that did not happen. Bundling them means the whole thing either happens or it does not.
What it means for your integration
If you are building the PSP side, do not model funding and payment as two loosely coupled calls that you sequence yourself. The scheme defines the combined operation, and the end-to-end flows describe how it settles. Your job is to implement the flow, not to invent your own orchestration on top of two primitives.
The practical consequence: a payment can succeed even when the payer's digital euro balance at the moment of initiation was zero, provided a linked account is in place. For business users — holding limit of zero, linked account mandatory — this is not an edge case. It is every single transaction.
Sources
Related reading
Acquiring PSP
An acquiring PSP serves business digital euro users — managing merchant accounts and the acceptance solutions through which businesses take payments.
Alias
An alias is a pseudonymous identifier — such as a phone number — standing in for a digital euro account, so you can be paid without revealing your DEAN.
BEAN
BEAN is the Basic Euro Account Number — positions 5 to 18 of a DEAN, the indicator digit plus the 13-digit serial.
CPACE
CPACE is the standard that applies to digital euro contactless NFC payments at the point of interaction, rather than a proprietary card-scheme protocol.