Unconfirmed picking quantity &1 large remaining quantity &2 &3 &4

What causes this issue?

During the split, an attempt was made to reduce the quantity of a
delivery item to the point that it became less than the quantity that
was picked but must still be confirmed.

System Response

The system does not allow subsequent delivery splits in this situation.

How to fix this error?

You can do one of the following:
Confirm the quantity that has yet to be picked correspondingly
Reduce the quantity that has yet to be picked correspondingly
Carry out the split in such a way that the split results and the split
complement are switched (opposite of how they appear now):
If the split result is to keep the original delivery number, execute
the split so that the split remainder is assigned the new delivery
number.
The opposite is true if the split result is to be assigned a new
delivery number.

Error message extract from SAP system. Copyright SAP SE.