work on muti purpose voucher

doc/appendix-de-kassensichv/receipt-case-definitions/receipt-case-definitions.md

@@ -17,5 +17,6 @@ Handling the issuance and redemption of single purpose vouchers depends on the t
 
 2. On the other side, if she operates a business with profit determination in regards of **§ 4 Abs. 3 EStG** than she must consider the VAT as shoon as she issues the voucher. In this case one of the following VAT specific charge item cases can be used for issuance: `0x4445000000000061`, `0x4445000000000062`, `0x4445000000000063`, `0x4445000000000064`, `0x4445000000000066` or `0x4445000000000067`. And for redemption the charge item case `0x444500000000006D`should be used.
 
+The issuance of multi purpose vouchers is covered by the charge item case (`ftChargeItemCase`): `0x4445000000000060`. Since there is no specific product or service coverded by the voucher the issuance is not taxable and no VAT rate must be specified. Same applies for redemption since the VAT rate is included in the charge items for the products or services of the request. For redemption of a multi purpose voucher, one can use the charge item case (`ftChargeItemCase`): `0x4445000000000068`. 
 
-The issuance of multi purpose vouchers is covered by the charge item case (`ftChargeItemCase`): `0x4445000000000060`. Since there is no specific product or service coverded by the voucher the issuance is not taxable and the VAT rate must be specified on redemption.
+For the issuance and redemption of a multi purpose voucher, you can also alternatively use pay items instead of charge items. The pay item case (`ftPayItemCase`) to be used is `0x444500000000000D`. Negative amounts get converted to an issuance, positive amounts get converted to a redemption.