Save time & contact JDE. They seem to be the only ones with this type of information and I don't think it is written down anywhere. I spent hours looking for required fields for a different app and could not find anything so I called and got the answer in 10 minutes.
check the knowledge garden for a pdf-file "Data Interface for Edlectronic Data Interchange". The file I have is from september 2000 (XeEAED.pdf). For every message, crucial information is entered.