I have this typical UI to edit Packages and it’s childs Shipments

Example URL for editing pckage is: /Packages/Edit/5

Now after clicking AddShipment my adress changes to eg: /Packages/AddShipmentForPackage, what makes app unable to refresh.
I’d like to add, remove end edit packages without changes in URL.

This is part of my Edit.cshtml:

<table class="table">
    <thead>
        <tr class="row">
            <th class="col-4">@Html.DisplayNameFor(model => model.Package.Shipments.First().ShipmentName)</th>
            <th class="col-3">@Html.DisplayNameFor(model => model.Package.Shipments.First().DeliveryAddress)</th>
            <th class="col-3">@Html.DisplayNameFor(model => model.Package.Shipments.First().CreatedDate)</th>
            <th class="col-1">@Html.DisplayNameFor(model => model.Package.Shipments.First().Weight)</th>
            <th class="col-1"></th>
        </tr>
    </thead>
    <tbody>
        @for (int i = 0; i < Model.Package.Shipments.Count; i++)
        {
            <tr class="row">
                @Html.HiddenFor(m => m.Package.Shipments[i].ShipmentId)
                @Html.HiddenFor(m => m.Package.Shipments[i].PackageId)
                <td class="col-4">
                    <input asp-for="@Model.Package.Shipments[i].ShipmentName" class="form-control" />
                </td>
                <td class="col-3">
                    <input asp-for="@Model.Package.Shipments[i].DeliveryAddress" class="form-control" />
                </td>
                <td class="col-3">
                    <input asp-for="@Model.Package.Shipments[i].CreatedDate" class="form-control" />
                </td>
                <td class="col-1">
                    <input asp-for="@Model.Package.Shipments[i].Weight" class="form-control" />
                </td>
                <td class="col-1">
                    <button type="submit" asp-action="RemoveShipmentForPackage" asp-route-id="@Model.Package.Shipments[i].ShipmentId" class="btn btn-danger"><i class="bi bi-trash"></i></button>
                </td>
            </tr>                                    
        }
    </tbody>
</table>                    
<div class="package-form--add-shipment">
    <button type="submit" asp-action="AddShipmentForPackage" class="btn btn-success">Add Shipment</button>
</div>

and this are my methods from controller:

[HttpPost]
public async Task<IActionResult> Edit(int id, PackageViewModel packageViewModel)
{
    var package = packageViewModel.Package;
            
    try
    {
        await _repo.EditPackageAsync(package, packageViewModel.GetShipmentsToRemove());
    }
    catch (DbUpdateConcurrencyException e)
    {
        ViewBag.ErrorMessage = e.Message;
        return View("Edit", package);
    }
    return RedirectToAction(nameof(Index));            
}

[HttpPost]
public IActionResult AddShipmentForPackage(PackageViewModel packageViewModel)
{
    packageViewModel.Package.Shipments.Add(new Shipment
    {
        ShipmentId = 0,
        ShipmentName = "",
        DeliveryAddress = "",
        CreatedDate = DateTime.Now,
        Weight = 0
    });
    var view = View("Edit", packageViewModel);
 
    return View("Edit", packageViewModel);
}

[HttpPost]
public IActionResult RemoveShipmentForPackage(int id, PackageViewModel packageViewModel)
{
    packageViewModel.Package.Shipments.RemoveAll(s => s.ShipmentId == id);

    packageViewModel.AddShipmentToRemove(id);
    return View("Edit", packageViewModel);
}