Ajax request not return branches drop down List based on company drop

I working on MVC razor page with .NET core 7 .I face issue Ajax request not return branches drop down list based on selected value from drop down list country .

with another meaning I need cascade branch drop down list based on country drop down list by using ajax request .

so data display data on branches drop down list will be

select iBranchCode,vBranchDesc from branchs  where companyno=companyno (selected value on drop down list company)

I try but not give me result

1-create model branches

public class Branch
{
    [Key]
    public string iBranchCode { get; set; }
    public string vBranchDesc { get; set; }
    public string CompanyNo { get; set; }
    public string CompanyName { get; set; }
}

2- on razor page AddUser.cshtml.cs

public class AddUserModel : PageModel
{
[BindProperty]
public UC.ADC.Core.Entities.SQL.User  User { get; set; }
private readonly ADCContext _db;
    public AddUserModel(ADCContext db)
    {
        _db = db;
        userModel = new AddUserViewModel();
      
    }
    public void OnGet()
    {
        userModel.Branches  = _db.Branch.ToList();
        userModel.Companies = GetCompanies();
    }
    public JsonResult GetRelatedBranches(string companyId)
    {
        var Branches = _db.Branch.Where(p => p.CompanyNo == companyId).ToList();

        return new JsonResult(Branches); 
      
    }
}

3-on html page of AddUser.cshtml

@page "/AddUser"
@model UC.ADC.Host.Pages.Users.AddUserModel
 

        

            Company
            

                
                    -- Select Company --
                     @foreach (var company in Model.userModel.Companies)
                     {
       
                        @company.CompanyName


                     }
                
            
        

        

            Branch
            

                
                    -- Select Branch --
                 @*   @(model.br == branch.Id ? "selected" : "")*@
                     @foreach (var branch in Model.userModel.Branches)
                    {
                        @branch.vBranchDesc
                    }