How to Create the Transfer Order with secondary Unit of Measure

Summary

Create the Transfer Order with secondary Unit of Measure

Content

Dear, 

We have one item call "Panadol001" the primary UOM is "Box30" and secondary UOM  is "EACH". So when I create the Transfer order request so by default system display the default primary UOM "Box30", which we cannot change/edit to secondary UOM. 

Also as a workaround, I suggest to the user to convert the quantity manually from box to each and enter fraction quantity, its also system is not allowing. 

Please advise based on your experience and knowledge that how the system will allow to the user  to enter the Internal Request by secondary UOM quantity?