Validation issue for BG

[essamik]

Hi there,

I noticed an error on the checksum validation of BG VAT Numbers, take for example BG202320104. It works on the VIES VAT number validation
website:

But on the library it fails when calling public static VatValidationResult IsValid(string vat)
Internally in BgVatValidator the checksum returns 9 instead of 11 or 10 and then it fails:

    private static VatValidationResult Validate9DigitVat(ReadOnlySpan<char> vatSpan)
    {
        var sum = vatSpan.Sum(MultipliersPhysicalPerson);

        var checkDigit = sum % 11;
        if (checkDigit == 10)
        {
            sum = 0;
            for (var index = 0; index < 8; index++)
            {
                sum += vatSpan[index].ToInt() * (index + 3);
            }
            checkDigit = sum % 11;
            if (checkDigit == 10)
            {
                checkDigit = 0;
            }
        }

Thanks