That would be a country specific thing &amp; is a bit of an outlier. As a simplified example though - sometimes the sales tax &#x2F; VAT is calculated as 10&#x2F;110 instead of 10&#x2F;100 (or vice versa depending on law). Or there is some small piece of info missing that technically means the invoice isn&#x27;t a legal tax invoice which means whoever you issued it to claims tax on that illegally (again country specific).<p>It&#x27;s unfortunately a case of people dont know how much they don&#x27;t know.