You need to leave the product code blank and select own packaging enter own package dimensions (I just put satchel dimensions)   The express post platinum choice then appears - it can only be paid when lodged or on-line with courier pickup.

No, i was not asking how to process a parcel through C&S.  I was asking how come that the option to offer Express Post Platinum Parcel is not available in the drop down menu when I am selecting the postage options for my listing.

The flat rate is for satchels, not for parcels; the rate for parcels varies from about $17 within Victoria, to $50something to Sydney, and $70 something to Brisbane.  There is no way I can use the flat rate option and just put there a  number.