UOM should be stated by using recommendation 20 v10

Namespace
cbc urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2
Data type
udt:QuantityType
Example value
1000
Attributes
Use Name Description
M @unitCode

Quanitity unit code

Example value: MLT

M @unitCodeListID

Quantity Unit. Code List Identifier
The list identifier for the unit of the quantity

Fixed value: UNECERec20

Rules
Identifier/Error message Flag
EUGEN-T68-B12701
Attribute 'unitCode' MUST be present.
fatal
EUGEN-T68-B12704
Attribute 'unitCodeListID' MUST be present.
fatal