The unit price, exclusive of VAT, before subtracting Item price discount, can not be negative
cbc urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2123.45| Use | Name | Description | 
|---|---|---|
| M | @currencyID | 
         Mandatory attribute. Use BT-5 
            Example value:   | 
| Identifier/Error message | Flag | 
|---|---|
| BR-28 The Item gross price (BT-148) shall NOT be negative.  | 
            fatal | 
| BR-CL-03 currencyID MUST be coded using ISO code list 4217 alpha-3  | 
            fatal |