Posted on October 2, 2026
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The six most common e-invoicing mistakes are: mistaking a normal PDF for an e-invoice, missing mandatory details such as a VAT ID or address, an invalid ZUGFeRD profile, a PDF view that disagrees with the XML data, archiving only the PDF picture instead of the XML data — and putting the switch off until just before the deadline. Most of them, if it comes to it, cost your client the input VAT deduction rather than you — and cost you your reputation.
A PDF by email isn't an e-invoice; it's an "other invoice". Until the end of 2026 (end of 2027 for smaller businesses) that's still allowed with the client's consent — after that, it isn't. Background: What Is an E-Invoice?
Software notices immediately when something's missing: your VAT ID, the client's address, a date of service. What might never have stood out on paper leads to a query or a rejection with an e-invoice.
The MINIMUM and BASIC-WL profiles don't contain all mandatory details and don't count as e-invoices. Look for the EN 16931 profile (formerly COMFORT) or higher.
With ZUGFeRD, the XML part is the legally binding one. If you edit the PDF afterwards — say, correcting an amount in a PDF editor — you create an invoice whose view no longer matches its data. Always correct the invoice itself and regenerate it.
For incoming and outgoing e-invoices alike, the structured data must be kept unchanged in its original format. A printout or a PDF without the embedded XML file isn't enough. More: Archiving E-Invoices
The switch itself rarely takes long. What takes time is the data: missing VAT IDs for clients, outdated addresses, invoice templates without a date of service. Sort that out in the autumn and you'll start January relaxed.
A trades business sent its first e-invoices with a simple online generator that only produced the BASIC-WL profile. The client's accounts department rejected all of them. Only on the second attempt — with complete client data and the EN 16931 profile — did the invoices go through.
Go through the six points and mark the one most likely to apply to you. In most cases it's number 2 — and that's an hour of data clean-up.
What happens if my client rejects my e-invoice? You have to issue a corrected invoice. Until then, payment is usually delayed.
How do I find out which ZUGFeRD profile my invoice uses? The profile is stated in the embedded XML file. Many e-invoice viewers display it directly; SmoovOps always generates the EN 16931 profile.
Can a faulty e-invoice cost my client money? Yes. If mandatory details are missing or the format is wrong, the client can only claim the input VAT once a correct invoice exists.
Note: This article is not tax advice. The binding sources are the German Federal Ministry of Finance and your IHK (chamber of commerce) (both in German); for your specific case, ask your tax advisor.
All of it in 13 pages: Get our free booklet E-Invoicing, Compact as a PDF – with the decision tree, a mistakes check and a switch-over plan – and receive the SmoovOps newsletter. → Get the booklet