What it means
When the seller and the buyer are both in Germany, the external document location (BT-124) must be an absolute URL with a valid scheme. That means the whole address including its start, such as https://, and not a file name, a relative path or an address that begins with www. The link points to a supporting document that sits online instead of being attached to the invoice.
Why it matters
The link lets the buyer open a supporting document, such as a timesheet or a delivery note, that is stored elsewhere. A link without a scheme usually does not open from the buyer's software. The file is still accepted, but it is worth fixing if the buyer needs that document to check the invoice.
How to fix it
Find the field for the external document link in your invoicing software, where you refer to a supporting document by web address. Replace the value with the full address starting with https:// and open it in a browser to check that it works. If you have no real link, remove the entry, or attach the document to the invoice instead of linking to it.
The rule as published
Read the rule on the publisher's site
Business terms: BT-124
Where this rule applies
| Rule set | Version |
|---|---|
| Peppol BIS Billing 3.0 (invoice) | 2026.5 |
| Peppol BIS Billing 3.0 (credit note) | 2026.5 |
Check your file
Drop your e-invoice to see whether DE-R-T02 still fails, and which other rules do.