Skip duplicate import record if invoice is in history

Running Sage 100 v2018.  Created a VI import into AP_InvoiceHeader/Detail in order to populate invoices into AP Invoice Entry.  I have a Perform that checks to see if there are duplicates in the AP_InvoiceHistoryHeader table:

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ENTRY_POINT:
IF NOT(coInvcHistHdr) THEN {
coInvcHistHdr = NEW("AP_InvoiceHistoryHeader_Svc",%SYS_SS)
}

InvoiceNo$ = VAR$

retExists =coInvcHistHdr'CheckInvoiceHistory(APDivisionNo$, VendorNo$, InvoiceNo$)

IF retExists THEN { VAR$=$$ }

EXIT

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This perform works great!  However, I would like to add a fourth validation for InvoiceDate$.  I must be missing something because when I add ", InvoiceDate$ to the end of the "retExists..." line, I end up with an Error 36 on the same line.  If I replace the "InvoiceDate$ with a different validation field (say replacing VendorNo$ with InvoiceDate$) I don't get the error...only when I'm adding a fourth validation.  It's got to be something I'm overlooking but can't seem to find it.