Unpacked item quantity &1 < unpacked quantity to be split &2 &3. &4

What causes this issue?

When you called up the subsequent delivery spit, partial quantities of
an item that are to be split were entered even though they are at least
partially packed. The system tries to assign these quantities to new
deliveries without reassigning the handling units correspondingly. In
this case, however, the quantity to be split is so large that the
delivery quantity would be less than the packed quantity.

System Response

The system does not allow the subsequent delivery split.

How to fix this error?

When you call up the split, enter the corresponding handling units.

Error message extract from SAP system. Copyright SAP SE.