Insert multiselect items with "SELECT MULTIPLE" into SQL Server using EF (ASP NET Core 2019)

Question

I'm trying to insert multiple elements chosen by user in <SELECT multiple> into a SQL Server database .

This is my code:

public class RegisterModel : PageModel
{
    private readonly DataAuthDbContext _blogeurContext;
    public List<SelectListItem> Options { get; set; }

    public class InputModel
    {
          ....
          public List<int> FavoriteMovieIds { get; set; }
    }

    public async Task OnGetAsync(string id, string returnUrl = null)
    {
        ReturnUrl = returnUrl;
        ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync()).ToList();
      
        Options = _blogeurContext.TLocalites.Select(a =>
                              new SelectListItem
                              {
                                  Value = a.TTerritoireID.ToString(),
                                  Text = a.Nom
                              }).ToList();
    }
......
}

and this is my view

<div class="row">
    <label asp-for="Input.FavoriteMovieIds">Type de structure :</label>
    <select asp-for="Input.FavoriteMovieIds" class="input-sm Editors"
            asp-items="Model.Options" multiple data-placeholder="Ajouter une zone d'intervention"></select>
    <span asp-validation-for="Input.FavoriteMovieIds" class="text-danger"></span>
</div>

The list is displaying the data very well, I want to know how to insert the data which the user has chosen into my database

I'm trying this in my post method,

public async Task<IActionResult> OnPostAsync(LocaliteChosie[] l, string? id, string returnUrl = null )
{
     ....
     var zoneIntervention = new TZonesIntervention
                        {
                            TIdentificationActeurID = user.Id,
                            TZonesInterventionId = cleZoneIntervention,
                            TLocalitesID = item.TLocalitesID,
                        };
     await _blogeurContext.TZoneIntervention.AddAsync(zoneIntervention);
     await _blogeurContext.SaveChangesAsync();
}

but it only insert one choice even if the user has chosen several.