Solution : https://service.sap.com/sap/support/notes/156883 (SAP Service marketplace login required)
Key words : 
additional key words wmmbid01, function module l_idoc_input_wmmbxy expect, exit function module exit_sapllmde_002, function module unit_of_measure_iso_to_sap, message type wmmbxy, sap internal format, sap enhancement mwmido08, idoc terminates, error mm107, alternative unit
Related Notes : 
       
| 747422 | Replace internal units with ISO codes - modification | 
| 521427 | FAQ: IDocs for goods movements | 
| 318976 | Transferring values to IDoc WMMBXY | 
| 166547 | LSR/MOB interface IDocs and ISO codes |