Send WhatsApp message to selected (checked) GridView rows using C# in ASP.Net

how to send whatsapps Msg Using c# in asp.net

I want to write wtsups sms in textarea and select number from gridview.

while user click on Whatsapp then whatsapp msg sent to destination number.

    <form id="form1" runat="server">
        <div class="auto-style1">
            <strong>
            <span class="auto-style4">&nbsp;Message System</span></strong><span class="auto-style2"><br class="auto-style3" />
            </span>
            <br />
        </div>
        <strong><span class="auto-style5">Message: </span></strong> <br />
        <div>&nbsp;<textarea id="TextArea1"></textarea>
        <br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <br />
       <div>
        <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" AllowPaging="true"
            OnPageIndexChanging="OnPageIndexChanging" PageSize="10">
            <Columns>
                <asp:BoundField ItemStyle-Width="150px" DataField="VEND_EMP" HeaderText="VEND_EMP" />
                <asp:BoundField ItemStyle-Width="150px" DataField="VEN_EMP_NAME" HeaderText="VEN_EMP_NAME" />
                <asp:BoundField ItemStyle-Width="150px" DataField="VEN_EMP_PHNO" HeaderText="VEN_EMP_PHNO" />
                <asp:BoundField ItemStyle-Width="150px" DataField="VEN_EMP_EMAIL" HeaderText="VEN_EMP_EMAIL" />
                 <asp:TemplateField HeaderText="CheckAll">
                     <HeaderTemplate>All
                        <asp:CheckBox ID="chkSelectAll" runat="server"
                                      AutoPostBack="true"
                                      OnCheckedChanged="chkSelectAll_CheckedChanged" />
                    </HeaderTemplate>
                        <ItemTemplate>
                        <asp:CheckBox ID="chkSelect" runat="server" Checked="false"/>
                        </ItemTemplate>
                     </asp:TemplateField>
            </Columns>
        </asp:GridView>
        <br />
        <br />     
        <asp:Button ID="Button2" runat="server" Text="Whatsapp" OnClick="Button2_Click"/>
    </div>
    </form>