DevOps, CI/CD and Automation

Bit of a noob question I'm afraid... I've had a look on t'interweb on in these forums and it has got me so far, but I'm doing something wrong.

I've managed to run procedures with an output parameter, but a return value from a function is sufficiently different to stump me.

Set oParam = .CreateParameter("iSequenceNo", adInteger, adParamReturnValue)
.Parameters.Append oParam

Set oParam = .CreateParameter("sSerialNo", adVarchar, adParamInput, 50, sSerialNo)
.Parameters.Append oParam

Set oParam = .CreateParameter("sPartNo", adVarchar, adParamInput, 50, sPartNo)
.Parameters.Append oParam

.CommandText= "{? = Call IFSAPP.Part_Serial_History_API.Get_Latest_Sequence_No(?, ?)}"
.Execute()

.Parameters.Delete "sSerialNo"
.Parameters.Delete "sPartNo"

I understand in this scenario that the Return Value must be the first parameter supplied.
When I run my code, it completes without any errors, but iSequenceNo is not populated. I assume the problem is the way in which I am calling the function, but I'm not sure what exactly is wrong.

Any help would be appreciated.

Thanks

Chris