What is the best approach to insert data to an external SQL database?

Thanks Scott, this is really helpful, and much appreciated for taking the time to respond.

I've now got my classes more organised, and everything from a syntax perspective I believe is correct, however, I am still running into an issue when the BusinessOperation tries to bind the parameters, and I believe it's something to do with me using varchar (max) in my SQL table.

There actual error text is this:

ERROR #6022: Gateway failed: BindParameters. 
ERROR <Ens>ErrGeneral: SQLState: (HY104) NativeError: [0] Message: [Microsoft][ODBC Driver 18 for SQL Server]Invalid precision value

The same error occurs regardless of SQL ODBC driver I use, so I get the impression the issue is actually with the BusinessOperation, rather than with the ODBC or database.

When I run the stored procedure directly in SSMS with the exact same data contained within the "PatientRequest" (listed below) object it runs without any issues, so that rules out a stored procedure issue in my eyes.

Here is my basic BusinessOperation:

Class JWDEV.SQLTesting.JWDEVBusinessOperation Extends Ens.BusinessOperation 
{ 

Parameter ADAPTER = "EnsLib.SQL.OutboundAdapter"; 

Property Adapter As EnsLib.SQL.OutboundAdapter; 

Parameter INVOCATION = "Queue"; 

Method OnMessage(pRequest As JWDEV.SQLTesting.PatientRequest, Output pResponse As JWDEV.SQLTesting.PatientResponse) As %Status 
{ 
    Try{ 

        Set query = "{call dbo.sp_insert_or_update_radiologyreports(?,?,?,?,?,?,?,?,?)}" 
        Set params = 9 
        Set params(1) = pRequest.patientid 
        Set params(2) = pRequest.accession 
        Set params(3) = pRequest.patientname 
        Set params(4) = pRequest.dob 
        Set params(5) = pRequest.sex 
        Set params(6) = pRequest.placerordernumber 
        Set params(7) = pRequest.universalserviceid 
        Set params(8) = pRequest.observationtext 
        Set params(9) = pRequest.observationdatetime 
        Set status = ..Adapter.ExecuteProcedureParmArray(,,query,"iiiiiiiii",.params) 

        If $$$ISERR(status){ 
            $$$LOGERROR($SYSTEM.Status.GetErrorText(status)) 
            Return status 
        } 
        Return status 

    } Catch(ex) { 
        Set status = ex.AsStatus() 
        $$$LOGERROR($SYSTEM.Status.GetErrorText(status)) 
        return status 
    } 
} 

} 

Here is the Request Class:

Class JWDEV.SQLTesting.PatientRequest Extends Ens.Request 
{ 

Property patientid As %String(MAXLEN = 50); 

Property accession As %String(MAXLEN = 50); 

Property patientname As %String(MAXLEN = 200); 

Property dob As %String(MAXLEN = 25); 

Property sex As %String(MAXLEN = 10); 

Property placerordernumber As %String(MAXLEN = 25); 

Property universalserviceid As %String(MAXLEN = 150); 

Property observationtext As %String(MAXLEN = ""); 

Property observationdatetime As %String(MAXLEN = 25); 

Storage Default 
{ 
<Data name="InsertDataDefaultData"> 
<Subscript>"InsertData"</Subscript> 
<Value name="1"> 
<Value>name</Value> 
</Value> 
<Value name="2"> 
<Value>mrn</Value> 
</Value> 
<Value name="3"> 
<Value>patientid</Value> 
</Value> 
<Value name="4"> 
<Value>accession</Value> 
</Value> 
<Value name="5"> 
<Value>patientname</Value> 
</Value> 
<Value name="6"> 
<Value>dob</Value> 
</Value> 
<Value name="7"> 
<Value>sex</Value> 
</Value> 
<Value name="8"> 
<Value>placerordernumber</Value> 
</Value> 
<Value name="9"> 
<Value>universalserviceid</Value> 
</Value> 
<Value name="10"> 
<Value>observationtext</Value> 
</Value> 
<Value name="11"> 
<Value>observationdatetime</Value> 
</Value> 
</Data> 
<DefaultData>InsertDataDefaultData</DefaultData> 
<Type>%Storage.Persistent</Type> 
} 

} 

Here is my SQL table schema:

[PatientID] [nvarchar](50) NOT NULL, 
[AccessionNumber] [nvarchar](50) NOT NULL, 
[PatientName] [nvarchar](200) NOT NULL, 
[DOB] [nvarchar](25) NOT NULL, 
[Sex] [nvarchar](10) NOT NULL, 
[PlacerOrderNumber] [nvarchar](25) NOT NULL, 
[UniversalServiceID] [nvarchar](150) NOT NULL, 
[ObservationText] [nvarchar](max) NOT NULL, 
[ObservationDateTime] [nvarchar](25) NOT NULL, 
[DateTimeInserted] [datetime] NOT NULL, 
 CONSTRAINT [PK_Radiology_Reports] PRIMARY KEY CLUSTERED 
( 
[PatientID] ASC, 
[AccessionNumber] ASC 
)

I'm not sure whether varchar (max) needs to be handled different compared to other varchar types in ObjectScript. I did see it was possible to explicitly define parameter types within "Specifying Parameters in an InterSystems IRIS Multidimensional Array", and I had attempted this, but I've not had any success as of yet.

Have you had any experience with this error or how to correctly handle varchar (max) datatypes in ObjectScript?