public class Project
    {
        [Key]
        [MaxLength(32)]
        public string ID { get; set; }
        public string Name { get; set; }
        public int Order { get; set; }
        public ICollection<UserStory> Stories { get; set; }
        public ApplicationUser Creator { get; set; }
        public DateTime CreateTime { get; set; }
        public ApplicationUser Modifier { get; set; }
        public DateTime UpdateTime { get; set; }
    }

public ICollection<UserStory> Stories { get; set; }

 warning CS0169: The field 'UserStoryController.mystr' is never used 
 System.Data.SqlClient.SqlException: Column 'Project.ID' is not the same length or scale as referencing column 'UserStories.ProjectID' in foreign key 'FK_UserStories_Project_ProjectID'. Columns participating in a foreign key relationship must be defined wit h the same length and scale.
Could not create constraint or index. See previous errors.
    at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
    at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) 
    at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) 

            migrationBuilder.AddColumn<string>(
                name: "ProjectID",
                table: "UserStories",
                maxLength:32,
                nullable: true);

        public async Task<IActionResult> Create(UserStoryViewModel userStoryViewModel)
        {
            if (ModelState.IsValid)
            {
                //mapping   
                UserStory usNew = map.Map<UserStory>(userStoryViewModel);
                usNew.ID = Guid.NewGuid().ToString("N");
                usNew.StatusCode = "Unstarted";
                usNew.Creator = _userManager.FindByNameAsync(User.Identity.Name).Result;
                usNew.CreateTime = DateTime.Now;
                usNew.Order = _context.UserStories.Max(t => t.Order)+1;
                _context.UserStories.Add(usNew);
                await _context.SaveChangesAsync();
                return RedirectToAction("Index");
            }
            return View("OK");
        }

<a asp-action="ViewStories" asp-route-id="@item.ID">View Stories</a>