SAP Business One Update Checks For Payment using SDK

What is the correct way to update IN SAP B1 using SDK. I am trying to update the status of checks for payment but it's not updating. Anyone has example how to update using SDK?

This is my code

                     sCheckKey = oForm.Items("grdChecks").Specific.DataTable.Columns.item(0).Cells.item(i).Value

                    Set oChecks = gDI.GetBusinessObject(oChecksforPayment)

                    If oChecks.GetByKey(sCheckKey) Then

                    oChecks.UserFields.fields.item("Printed").Value = "Y"

                    oChecks.Update

                    End If

Thank you.

Regards,

Raphael