The revenue account determines where the income is recorded. This keeps different types of revenue visible in your results and reports.
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The VAT code determines not only the rate but also where an amount appears in the VAT return. Two lines with the same rate may still require different tax treatment.
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A product or default setting can prefill these choices. Always review them when the supply, customer or VAT situation differs. If in doubt, have the line reviewed instead of guessing.