Fix BR-DE-18 cash-discount terms

Use the structured terms

For XRechnung cash-discount terms, use uppercase hash-separated SKONTO, TAGE and PROZENT segments. The percentage needs two decimal places. Add BASISBETRAG only where the discount applies to part of the amount due.

The newline is part of the value

The example #SKONTO#TAGE=10#PROZENT=2.00# must be followed by an actual newline. A literal backslash and n are two characters, not a newline. Use the actual discount agreement; this example is not a recommended payment condition.

Export and recheck

Some editors remove trailing newlines when saving or exporting. Check the resulting BT-20 value rather than relying on how a text area looks. Inspect the exported original against its stated ruleset. See BR-DE-18.