Code specifying the additional allowance, see code list at https://big.btwentyfour.com/codes#id3
invoic_Examples
<allowances name="unspecified allowance" code="ACA" percent="10" amount="40.00" />
invoic_XPATH
/b24Message/invoice/allowances/@code
invoic_Required
No
invoic_Type
Text
invoic_Sort
23200