Renamed everything from MultiShop to Props.

Props/server/Pages/Error.cshtml

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+@page
+@model ErrorModel
+@{
+    ViewData["Title"] = "Error";
+}
+
+<h1 class="text-danger">Error.</h1>
+<h2 class="text-danger">An error occurred while processing your request.</h2>
+
+@if (Model.ShowRequestId)
+{
+    <p>
+        <strong>Request ID:</strong> <code>@Model.RequestId</code>
+    </p>
+}
+
+<h3>Development Mode</h3>
+<p>
+    Swapping to the <strong>Development</strong> environment displays detailed information about the error that occurred.
+</p>
+<p>
+    <strong>The Development environment shouldn't be enabled for deployed applications.</strong>
+    It can result in displaying sensitive information from exceptions to end users.
+    For local debugging, enable the <strong>Development</strong> environment by setting the <strong>ASPNETCORE_ENVIRONMENT</strong> environment variable to <strong>Development</strong>
+    and restarting the app.
+</p>

Props/server/Pages/Error.cshtml.cs

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+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using Microsoft.Extensions.Logging;
+
+namespace Props.Pages
+{
+    [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
+    public class ErrorModel : PageModel
+    {
+        private readonly ILogger<ErrorModel> _logger;
+
+        public ErrorModel(ILogger<ErrorModel> logger)
+        {
+            _logger = logger;
+        }
+
+        public string RequestId { get; set; }
+
+        public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
+
+        public void OnGet()
+        {
+            RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier;
+        }
+    }
+}

Props/server/Pages/Shared/_LoginPartial.cshtml

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+@using Microsoft.AspNetCore.Identity
+@using Props.Models;
+@inject SignInManager<ApplicationUser> SignInManager
+@inject UserManager<ApplicationUser> UserManager
+
+@{
+    string returnUrl = null;
+    var query = ViewContext.HttpContext.Request.Query;
+    if (query.ContainsKey("returnUrl"))
+    {
+        returnUrl = query["returnUrl"];
+    }
+}
+
+<ul class="navbar-nav">
+    @if (SignInManager.IsSignedIn(User))
+    {
+        <li class="nav-item">
+            <a class="nav-link text-dark" asp-area="Identity" asp-page="/Account/Manage/Index" title="Manage">Hello @User.Identity.Name!</a>
+        </li>
+        <li class="nav-item">
+            <form class="form-inline" asp-area="Identity" asp-page="/Account/Logout" asp-route-returnUrl="/">
+                <button type="submit" class="nav-link btn btn-link text-dark">Logout</button>
+            </form>
+        </li>
+    }
+    else
+    {
+        <li class="nav-item">
+            <a class="nav-link text-dark" asp-area="Identity" asp-page="/Account/Register" asp-route-returnUrl="@returnUrl">Register</a>
+        </li>
+        <li class="nav-item">
+            <a class="nav-link text-dark" asp-area="Identity" asp-page="/Account/Login" asp-route-returnUrl="@returnUrl">Login</a>
+        </li>
+    }
+</ul>

Props/server/Pages/_ViewImports.cshtml

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+@using Props
+@namespace Props.Pages
+@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers