Razor page <input asp-for> only submits as null value for my class' int value, despite entering a value

I cannot seem to use integers with <input asp-for="" /> when creating a new Department instance, the value reverts to null when reaching OnPost(). I have no idea as to what the issue is,
<input asp-for="" /> works fine for the other value types within Department.

Department.cs

using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Diagnostics.CodeAnalysis;

namespace Scratch.Data
{
	public class Department
	{
		[Key]
		public int Id { get; set; }

		[Required]
		public string departmentName { get; set; }

		[Required]
		[ForeignKey("AspNetUsers")]
		public string departmentManagerId { get; set; }

		[AllowNull]
		[ForeignKey("AspNetUserRoles")]
		public string? managerRoleId;

		[AllowNull]
		[ForeignKey("AspNetUserRoles")]
		public string? userRoleId;

		[AllowNull]
		public int? defaultDisplayOrder;
	}
}

I simplified the code below down to testing for the one input I want to get from the page:

CreateDepartmentIntTestModel

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.Build.Evaluation;
using Microsoft.CodeAnalysis;
using Microsoft.EntityFrameworkCore;
using Scratch.Data;
using System.Text.RegularExpressions;
using Microsoft.AspNetCore.Mvc.TagHelpers;

namespace Scratch.Pages.Admin_Tools
{
	[BindProperties]
	[Authorize(Roles = "Administrators,ProjectManager")]
	public class CreateDepartmentIntTestModel : PageModel
	{
		private readonly ApplicationDbContext _db;
		

		private readonly UserManager<IdentityUser> _userManager;
		private readonly IUserStore<IdentityUser> _userStore;

		private readonly RoleManager<IdentityRole> _roleManager;
		private readonly IRoleStore<IdentityRole> _roleStore;

		public Department Department { get; set; }


		public CreateDepartmentIntTestModel(ApplicationDbContext db, UserManager<IdentityUser> userManager,
			IUserStore<IdentityUser> userStore,
			RoleManager<IdentityRole> roleManager,
			IRoleStore<IdentityRole> roleStore)
		{
			_db = db;
			_userManager = userManager;
			_userStore = userStore;
			_roleManager = roleManager;
			_roleStore = roleStore;

		}
	

		

		

		public async Task<IActionResult> OnGet()
		{
			
			return Page();

        }

		

		public async Task<IActionResult> OnPost()
		{

			
			//this is always null despite inputs
			if (Department.defaultDisplayOrder == null)
			{
				//add breakpoint here:
				ModelState.AddModelError("Department.defaultDisplayOrder", "display order is null");
			}


			

			

			return Page();
		}


		

	}
}

Html

@page
@model Scratch.Pages.Admin_Tools.CreateDepartmentIntTestModel
@{
}

<form method="post">
	
	<input hidden asp-for="Department.managerRoleId"   />
	<input hidden asp-for="Department.userRoleId"  />

	<div class="border p-3 mt-4">
		<div asp-validation-summary="All" class="text-danger"></div>
		<div class="row pb-2">
			<h2 class="text-primary pl-3">
				Test to enter a numeric value to department:
			</h2>
		</div>
		<div class="mb-3">

			Department Display Order Value:
			<input asp-for="Department.defaultDisplayOrder" class="form-control" />
			<span asp-validation-for="Department.defaultDisplayOrder" class="text-danger"></span>
			
			<hr/>
			

		</div>
		<button type="submit" class="btn btn-primary" style="width:150px;">Create</button>

	</div>
	
</form>

Your defaultDisplayOrder member is a field, not a property (ref: https://stackoverflow.com/questions/295104/what-is-the-difference-between-a-field-and-a-property). Model binding only works with public properties. Add { get; set; } to the declaration to make it a property:

public int? defaultDisplayOrder { get; set; }