Problem: Adding command argument to button - by listitem id

Hey, I have following problem:
I have a list of Inovices which each have an id, which I want to set as commandargument on a button, but I get an empty string, I have tried to google and have found I should use <%# eval(inovice.id.ToString()) %>, My page and code behinde looks like this:
Page:

<%@ Page Title="Contact" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="Inovices.aspx.cs" Inherits="SpeciallseringsWebpage.Inovices" %>

<asp:Content runat="server" ID="BodyContent" ContentPlaceHolderID="MainContent">
    
<table border="1">
    <thead>
        <tr>
            <th>Inovice number</th>
            <th>Date</th>
            <th>VIEW</th>
        </tr>
    </thead>
    <%SpecialliseringLibary.Customer customer = (SpecialliseringLibary.Customer) Session["customer"]; %>
    <%if(customer != null){
          int i = 1;
           %>
      <%foreach(SpecialliseringLibary.Inovice inovice in SpecialliseringLibary.Service.getInoviceByCustomerId(customer.id)){ %>
           <%
            if (i % 2 == 0) { 
            %>
                <tr>
            <%
            }else{  
           %>   
                <tr "background: #C0C0C0;" >    
           <%} %>
            
                <td>
                    <%= inovice.id.ToString() %>
                 </td>
                <td><%= inovice.Date.ToString() %>  

              </td> <%--"3034201A-69EA-4A03-BB5E-90620C899EEB"--%>
              <td>
                  <%string id = inovice.id.ToString();
                    Response.Write(id); %>
                  <asp:Button runat="server" Text="=>" onclick="btnViewInovice" CommandArgument=<%# inovice.ToString() %> /> <%--inovice.id.ToSTring())--%> 
             </td>
            </tr>
        <%
            i++;
        } %>
    <%} %>

</table>
</asp:Content>

Code behind

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace SpeciallseringsWebpage
{
    public partial class Inovices : Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (Session["customer"] == null) {
                Server.Transfer("Default.aspx");
            }
        }

        public void btnViewInovice(object sender, EventArgs e) {
            Button btn = (Button)sender;

            string id = btn.CommandArgument;
            Session["chosenInovice"] = id;
            Server.Transfer("overview.aspx");
        }
    }
}

Can anyone help - thanks in advance