An invoice merge is an implicit merge print. The header or parent data contains a record for each document, which is linked 1:n to the detail or child data. To design such an invoice and print/export it out, List & Label must be made aware of the parent table via the DataMember property. In addition, the AutoMasterMode property must be set to AsVariables, as shown in the following example. For more details on the use and distinction between variables (header data) and fields (parent data) when using the AutoMasterModer property, see also Variables, Fields and Datatypes.

using (ListLabel LL = new ListLabel())
{
    // Define/Assign data source
    LL.DataSource = CreateDataSet();

    // Order data as variables
    LL.DataMember = "InvoiceHeader";
    LL.AutoMasterMode = LlAutoMasterMode.AsVariables;

    // Call the Designer
    LL.Design();

    // Print
    LL.Print();
}

Using LL As New ListLabel()
    ' Define/Assign data source
    LL.DataSource = CreateDataSet()

    ' Order data as variables
    LL.DataMember = "InvoiceHeader"
    LL.AutoMasterMode = LlAutoMasterMode.AsVariables

    ' Call the Designer
    LL.Design()

    ' Print
    LL.Print()
End Using