An XInvoice can be technically flawless and still end up in manual review. The reason is rarely the format itself, but the reference fields: If the order number is missing, the cost item is incorrectly recorded, or a project reference is filled in inconsistently, even an automated system cannot assign the invoice to the correct process. This article sorts out which booking references are relevant and how to implement them consistently within your own company.

XRechnung Order number, Project number, Cost center: The relevant BT fields at a glance

The European accounting standard EN 16931 defines a series of reference fields that link an invoice with the upstream business process. For the invoice recipient, usually the client, the following fields are particularly relevant:

BT-10 Buyer reference: Leitweg ID, Commission, internal reference number

BT-11 Project reference: Project number

BT-12 Contract reference: Frame contract number

BT-13 Order number: Specific order, assigned by the buyer

BT-17 Tender or lot reference: Award number, identifier of the tender

BT-18 Object ID: Object number referenced in the invoice

BT-19 Buyer booking reference: Cost center or cost provider

On an item level, additional information is included: BT-155 (supplier’s item number), BT-156 (buyer’s item number) and BT-157 (EAN), which is particularly relevant when invoices need to be matched with orders with pinpoint accuracy.

It is important to distinguish between BT-12 and BT-13: BT-12 refers to a framework agreement, BT-13 to a single, specific order. Both fields are optional according to EN 16931, but in practice many receiver systems require at least one of them for automatic assignment, and this applies to XRechnung as well as for ZUGFeRD and Peppol-BIS-billing.

BT fields E-Invoicing: Why a uniform understanding across all industries matters

The challenge often lies not in the technical implementation of the fields themselves, but in the fact that clients and suppliers interpret the fields differently. If a company forms its own, individual requirements for invoicing, such as a specific field configuration that deviates from industry standard practice, the invoice may in the worst case only work with one recipient. This contradicts the basic idea of this standard: an e-invoice should work for every recipient regardless of who created it.

The standard EN 16931 Although it defines the meaning of the individual BT fields, it does not determine which reference a specific company actually needs or how this reference is generated internally. This translation work, ranging from the own cost structure to the ERP mapping and the binding communication with suppliers, remains an individual task. It depends on the existing system landscape, the customer structure, and often also on industry-specific peculiarities that go beyond the standard. A uniform understanding of the field meaning is the prerequisite for being able to even discuss references with business partners; the actual implementation of these is the actual work step thereafter.

The entire process chain counts, not just the invoice

Booking references do not only appear on the invoice; they are already created during the ordering process and must remain consistent throughout the entire process chain: from the quote to the ordering and order confirmation, to the delivery note and finally to the invoice. There are now suitable electronic formats for each of these steps, such as Order-X or Peppol-BIS Order for the ordering process, Deliver-X for the delivery note, and XRechnung, ZUGFeRD or Peppol-BIS Billing for the invoice itself.

The first step towards consistency is organizational: the department responsible for IT, the finance department, and the IT department should jointly determine which BT field takes which internal reference, document this association, and communicate it clearly to suppliers. This decision cannot be made by anyone from the outside; it depends on the own cost center structure and the existing processes.

The technical implementation, i.e. the continuous and seamless representation of these references across ERP systems, online stores, and other recording systems, all the way to invoices, is the more complex part. In practice, this is often the reason why companies rely on specialized solutions for this part of the process chain instead of developing their own: Any system change, any new supplier, and any different invoice format can again jeopardize consistency. Once the organizational assignment has been defined correctly, this creates the foundation on which this technical implementation can be reliably implemented.

What it costs when booking references are missing

The difference between well-prepared and unprepared invoice processing can be quantified by a key metric: the touchless rate, which is the proportion of invoices that go through without any manual intervention. According to the Billentis Market Report 2026, companies with sophisticated e-procurement processes and a consistent data base often achieve touchless rates of over 80 percent. The crucial factor behind this is precisely the consistent, consistent data base, which includes reference fields such as order number, project number, and cost center.

Conversely, this means that any invoice that cannot be automatically assigned due to a missing or inconsistent booking reference leaves this path and ends up in manual processing, with the corresponding costs in terms of personnel time, follow-up questions, and delays that already manifest themselves when considering the costs per invoice in their basic analysis. A high touchless rate is thus not an IT KPI in itself, but the direct result of how consistently reference fields are maintained from order to invoice. Companies that do not standardize their booking references are giving away a portion of the exact potential for automation that modern e-invoicing processing actually offers.

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