Field help (UOMSAIFLG) 

This setup is used to define, for this entry transaction, whether the entry in packing units is authorized or not in the receipt movement.

The specific case of Customer returns:

If the entry of PAC unit is allowed, then it is possible to modify the sales unit in the return by selecting a different sales unit among the following units:

Otherwise, the sales unit cannot be modified and the PAC/STK coefficient and the STK quantity fields are not displayed.

Special case ofLoan returns:

The entry in PAC is not possible in a load return line. The sales unit cannot be modified for this type of return.
However, for this type of document, the conversion coefficient between the document unit and the stock unit will always be displayed as well as the corresponding quantity in stock unit.