https://userapps.support.sap.com/sap/support/knowledge/en/2300802
2300802 - BADI ME_PROCESS_OUT_CUST is not called in ME31L/ME32L/ME31K/ME32K - SAP ERP & SAP S/4...
BADI ME_PROCESS_OUT_CUST is never called in transactions: ME31K,ME32K, ME31L , ME32L.