XRechnung 4.0: One invoice for several purchase orders

On Monday, a customer orders desk lamps. On Thursday, they order monitor arms. You deliver everything together and want to issue a single invoice. The amounts are correct and both purchase order numbers are included. Yet the customer’s accounts team might still ask: which invoice line belongs to which order?

This fictional example illustrates one of the changes planned for XRechnung 4.0. The preliminary specification allows an invoice to reference several purchase orders and deliveries. For businesses that regularly bill a customer for several orders at once, this is a development worth watching. KoSIT’s September 2026 announcement

Do you need to change anything now?

You do not need to switch to version 4.0 yet. As of 4 October 2026, only a preliminary version is available, and it is explicitly not intended for production use. The final release package is provisionally expected in spring 2027. Development status

According to KoSIT, XRechnung 3.0 will remain in force until at least 31 July 2027. The announcement therefore does not mean you need to change how you issue invoices immediately. Official version overview

The preliminary version is still useful as a preview: it shows which business processes the format is intended to describe more precisely. It does not yet establish whether your invoicing software and each recipient will support those capabilities.

Why putting both numbers on the invoice is not enough

Returning to the office equipment order, the intended relationship is simple:

Invoice line	Corresponding purchase order
20 desk lamps	PO-410
10 monitor arms	PO-587

The accounts team needs that relationship to check whether the goods were ordered and which purchase order the invoice settles.

If both numbers appear together in a notes field, someone may have to read the details manually or ask for clarification. An e-invoice is intended to carry these details in a form the recipient’s software can use. Being readable on an invoice and being available for automatic matching are therefore two different things.

The agreed invoice specification matters here. For example, the May 2026 release of Peppol BIS Billing 3.0 allows at most one purchase order reference at invoice level. That is a specific limitation of this specification, not a general statement that consolidated invoices are impossible. Peppol purchase order reference specification

The planned XRechnung change therefore provides more than extra room for text: it is intended to represent multiple order references explicitly within the invoice standard.

A new capability does not mean your customer has agreed to use it

Suppose your software can eventually include both purchase orders correctly in an XRechnung 4.0 invoice. Your customer might still require separate invoices for their internal processing. The standard describes what information a file can contain. You still need to agree with the customer how they will check orders and approve invoices.

A useful question for their purchasing team would be: “Can we invoice these two purchase orders together, and how should each invoice line be assigned?” This establishes more than simply asking whether the customer accepts e-invoices.

Changing invoice formats also deserves attention. If the destination format or the software used can only retain one purchase order reference, you need to establish what happens to the second. Including it in a note may help a person. Whether the accounting software can still recognise it automatically is another question.

An apparently simple solution would be to split the consolidated invoice into two. But that raises further questions: how should a shared discount be divided? Which invoice should a deposit be assigned to? Which invoice numbers should be used? Those decisions belong in the invoicing process and should not happen incidentally when a file is converted.

What to ask your software provider

If consolidated invoices are part of your day-to-day work, you can raise these questions before any changeover. The most useful starting point is an example with two purchase orders and clearly assigned invoice lines. Your provider can then explain:

Can the software assign each invoice line to its purchase order?
Is that relationship preserved in the e-invoice that is sent?
Is there a clear warning if the format required by the customer cannot represent it?

These questions are useful even if you continue with your current process for now. Clarifying the arrangement before your first consolidated invoice is easier than resolving a missing reference after the goods have been delivered and the invoice sent.

For now, the practical step is straightforward: use the invoice version accepted today and agree the billing arrangements with customers whose orders you want to combine. XRechnung 4.0 offers a new technical possibility; the arrangement with the recipient remains essential.