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Error message: "Für Beleg: 0/Position: 1 konnte kein gültiger MWST-Code mit dem MWST-Satz: 7.7 ermittelt werden."

The following error message appears if the VAT references are not set in the "621 Application Settings" program.
You can set this under "621 Application settings > Abacus Toolkit > VAT references".