Hi All
Just for anyone else who is wanting to know where to implement this, you need to change/validate the ECC order type in SRM before the number range is determined (the new PO number is added to the XML and depending on the Order type a different number range is used). We used the following to do the code in an enhancement point:
Class/Interface: CL_BBP_SC_TRANSFER_SOURCING
Method : INIT_SC_DATA
Regards
Wesley