Quantities and units of measure (table parameter &, line &) not permitted

What causes this issue?

You have entered a value in one of the following quantity fields in
line &V1& of table <ZK><ZH>Itemdata </></> (reference to a service PO
with non-service based invoice verification or reference to a blanket
PO), even though this is not permitted:
- Quantity (QUANTITY)
- PO unit of measure (PO_UNIT)
- PO unit of measure in ISO code (PO_UNIT_ISO)
- Quantity in PO price unit of measure (PO_PR_QNT)
- PO price unit of measure (PO_PR_UOM)
- PO price unit of measure in ISO code (PO_PR_UOM_ISO)

How to fix this error?

Enter an initial value in the all of the above quantity fields.

Error message extract from SAP system. Copyright SAP SE.