Get fieldByName Sage300 accpac session

Question

I want to integrate data from my sql DB to Sage 300 accpac

 

When getting PORCP1headerFields.FieldByName("RCPHSEQ")

 

returns Null object exception error

 

What I have tried:

public override void InsertInvoiceHeader()
{
    PORCP1header.Order = 1;
    PORCP1header.Order = 0;
    PORCP1headerFields.FieldByName("RCPHSEQ").SetValue("0", false);
    // Receipt Sequence Key
    PORCP1header.Init();
    PORCP1header.Order = 1;
    PORCP1detail1.RecordClear();
    PORCP1detail3.RecordClear();
    PORCP1detail4.RecordClear();
    PORCP1detail6.Init();
    PORCP1detail2.Init();
    sRcpSeq = PORCP1headerFields.FieldByName("RCPHSEQ").Value.ToString();
PORCP1headerFields.FieldByName("RCPNUMBER").SetValue(base.dsHeaders.Tables[0].Rows[base.counterIH]["RCPNUMBER"].ToString(), true); // RECEIPT NUMBER
}