Having some trouble here...
I'm a but unclear what to feed into the investFields for buy and sells it seems. I have:
'''
invFlds = InvestFields()
invFlds.txnType = InvestTxnType.BUY
invFlds.date = dateInt
invFlds.taxDate = dateInt

invFlds.secCurr = security
invFlds.security = acct

invFlds.hasShares = True
invFlds.shares = qty

invFlds.hasAmount = True
invFlds.amount = amount

invFlds.hasFee = False

enteredInt = DateUtil.getStrippedDate()
check = ''

txn = ParentTxn.makeParentTxn(book,dateInt,dateInt,enteredInt,check,acct,desc,memo,-1,ParentTxn.STATUS_RECONCILING)
invFlds.storeFields(txn)
txn.syncItem()
'''

if the 'acc' variable is set to the sub account for the security the resulting transaction looks like this (in the python console):
'''
[ParentTxn(b1a37ccf-19d5-4fce-839d-2fc8f879993d) 20200830 desc=AAPL; val=-234355; stat=x; #splits=1; chk=; acct=XXXXX:APPLE INC; splits=SplitTxn: val=11; amt=-234355; desc=; stat= ; cat=XXXXX:APPLE INC; tags=[(samt:11)(acctid:b57aabde-702e-4613-ae62-ca88e6352a08)(invest.splittype:sec)(obj_type:)(id:5438b295-3502-4f87-872f-fd0e9dede292)(pamt:-234355)(desc:)]; ], ; ]
'''
Looks promising, but in the Register in the Moneydance UI is blank. The transaction doesn't show up at all!
In the UI Security Details tab I see the transaction duplicated (it shows up twice).

I've also tried just feeing in the investment account for 'acct'. That creates and entry in the UI Register, but only the date and description are filled in. In pythin that transaction looks like:
'''
[ParentTxn(7ce81df3-064f-4217-b612-da427d3485db) 20200830 desc=AAPL; val=0; stat=x; #splits=0; chk=; acct=XXXXX; splits=; ]
'''
Any thoughts as to what I'm missing here?