Save multiple checkbox value to database in ASP.NET Core MVC

I am using checkboxes to save data in database. It can save only one value at a time. When multiple values are selected, it only stores the first selected value.

I have Googled my problem. Multiple solutions suggested the use of List<string> Name in Model. I tried to do so but my controller gave me error CS0029.

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• Database Table (CollectionCategories):

Id	CategoryName
1	First Category
2	Second Category
...	...

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Code-

• Model:

public class PostModel
{
    // Code before

    public string? CollectionCategory { get; set; }
}

public class CollectionCategoryModel
{
    [Key]
    public int Id { get; set; }
    public string CategoryName { get; set; }
}

• ViewModel:

public class CreatePostViewModel
{
    // Code before
    
    // Category
    public string? CollectionCategory { get; set; }

    // Category List
    public List<CollectionCategoryModel>? CollectionCategoryList { get; set; }
}

• Controller:

public async Task<IActionResult> CreateAsync()
{
    // Category List
    var CreatePostCategoryVM = new CreatePostViewModel
    {
        CollectionCategoryList = await _context.CollectionCategories.ToListAsync()
    };

    return View(CreatePostCategoryVM);
}

[HttpPost]
public async Task<IActionResult> Create(CreatePostViewModel postVM)
{
    if (ModelState.IsValid)
    {
        var post = new PostModel
        {
            // Code before             

            // Category
            CollectionCategory = postVM.CollectionCategory,
        };

         return RedirectToAction("Index");
    }
    else
    {
        // Error
    }
    return View(postVM);
}

---

• View:

<div class="form-check">
    @foreach (var list in Model.CollectionCategoryList)
    {
        <input type="checkbox" asp-for="CollectionCategory" id="@list.CategoryName" value="@list.CategoryName">
        <label asp-for="CollectionCategory" for="@list.CategoryName"> @list.CategoryName </label>
    }
</div>

---

Edited

Error:

(JsonReaderException: 'S' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 1.)

• Controller

[HttpGet]
public async Task<IActionResult> Index()
{
    var CardPostVM = new CardsViewModel
    {
        PostCard = await _context.Posts.ToListAsync()
    };

    var cached = _cache.TryGetValue("post", out var post);
    if (cached)
    {
        return View(post);
    }

    return View(CardPostVM);
}

• ViewModel

public class CardsViewModel
{
    public List<PostModel>? PostCard { get; set; }
    public List<CollectionModel>? CollectionCard { get; set; }
}

Error Image

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Thank you