Hi kid.live,

Please refer below sample.

HTML 

<table>
    <tr>
        <td>Branch Number:</td>
        <td><asp:TextBox runat="server" ID="txtBranchNumber" /></td>
    </tr>
    <tr>
        <td>Machine Number:</td>
        <td><asp:TextBox runat="server" ID="txtMachineNumber" /></td>
    </tr>
    <tr>
        <td><asp:Button Text="Search" runat="server" OnClick="Search" /></td>
    </tr>
</table>
<hr />

<asp:GridView runat="server" ID="gvDetails">

</asp:GridView>

Namespaces

C#

using System.Data;
using System.Net;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

VB.Net

Imports System.Data
Imports System.Net
Imports Newtonsoft.Json
Imports Newtonsoft.Json.Linq

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.BindData();
    }
}

protected void Search(object sender, EventArgs e)
{
    this.BindData();
}

private void BindData()
{
    ServicePointManager.Expect100Continue = true;
    ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072;
    string json = (new WebClient()).DownloadString("https://fuel-station-d8853-default-rtdb.firebaseio.com/invoices-prod.json");
    JToken result = JsonConvert.DeserializeObject("[" + json + "]") as JToken;
    List<Root> roots = new List<Root>();
    foreach (var item in result)
    {
        JObject obj = JObject.Parse(item.ToString());
        foreach (var keypair in obj)
        {
            foreach (var keypair1 in JObject.Parse(keypair.Value.ToString()))
            {
                foreach (var item1 in JObject.Parse(keypair1.Value.ToString()))
                {
                    roots.Add(JsonConvert.DeserializeObject<Root>(item1.Value.ToString()));
                }
            }
        }
    }
    if (!string.IsNullOrEmpty(txtBranchNumber.Text) || !string.IsNullOrEmpty(txtMachineNumber.Text))
    {
        roots = roots.Where(x => x.branch_num.StartsWith(txtBranchNumber.Text.Trim()) && x.machineID.StartsWith(txtMachineNumber.Text.Trim())).ToList();
    }
    gvDetails.DataSource = roots;
    gvDetails.DataBind();
}

public class Root
{
    public string branch_num { get; set; }
    [JsonProperty("date")]
    public DateTime _date { get; set; }
    public string invoice_number { get; set; }
    public string item { get; set; }
    public string machineID { get; set; }
    public string payment_type { get; set; }
    public double price { get; set; }
    public double qty { get; set; }
    public double total { get; set; }
    public string userID { get; set; }
    public double vat_amount { get; set; }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Me.BindData()
    End If
End Sub

Protected Sub Search(ByVal sender As Object, ByVal e As EventArgs)
    Me.BindData()
End Sub

Private Sub BindData()
    ServicePointManager.Expect100Continue = True
    ServicePointManager.SecurityProtocol = CType(3072, SecurityProtocolType)
    Dim json As String = (New WebClient()).DownloadString("https://fuel-station-d8853-default-rtdb.firebaseio.com/invoices-prod.json")
    Dim result As JToken = TryCast(JsonConvert.DeserializeObject("[" & json & "]"), JToken)
    Dim roots As List(Of Root) = New List(Of Root)()

    For Each item In result
        Dim obj As JObject = JObject.Parse(item.ToString())

        For Each keypair In obj

            For Each keypair1 In JObject.Parse(keypair.Value.ToString())

                For Each item1 In JObject.Parse(keypair1.Value.ToString())
                    roots.Add(JsonConvert.DeserializeObject(Of Root)(item1.Value.ToString()))
                Next
            Next
        Next
    Next

    If Not String.IsNullOrEmpty(txtBranchNumber.Text) OrElse Not String.IsNullOrEmpty(txtMachineNumber.Text) Then
        roots = roots.Where(Function(x) x.branch_num.StartsWith(txtBranchNumber.Text.Trim()) AndAlso x.machineID.StartsWith(txtMachineNumber.Text.Trim())).ToList()
    End If

    gvDetails.DataSource = roots
    gvDetails.DataBind()
End Sub

Public Class Root
    Public Property branch_num As String
    <JsonProperty("date")>
    Public Property _date As DateTime
    Public Property invoice_number As String
    Public Property item As String
    Public Property machineID As String
    Public Property payment_type As String
    Public Property price As Double
    Public Property qty As Double
    Public Property total As Double
    Public Property userID As String
    Public Property vat_amount As Double
End Class

Screenshot