ASP.NET azure hosted app / sql server Works on localhost only

Question

When I run my simple CRUD app on localhost it works really good.

Hint: It is using SQL server to insert data and server is hosted on my Azure Subscription inside same Resource Group

Deployed app : myAzureWebsitesLink.net

Not working route : School - Region - Countries

/Countries/CountriesIndex

On Azure SQL Server - Networking this is my props

appsettings.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "AZURE_SQL_CONNECTIONSTRING": "Server=tcp....database.windows.net,1433;Initial Catalog=myDB;Persist Security Info=False;User ID=myUser;Password=myPW;MultipleActiveResultSets=False;Encrypt=True;TrustServerCertificate=False;Connection Timeout=120;"
  }

CountriesController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using Models;

namespace Controllers
{
    public class CountriesController : Controller
    {
        private readonly ApplicationDbContext _context;

        public CountriesController(ApplicationDbContext context)
        {
            _context = context;
        }

        // GET: Products
        public async Task

Answer 1

Detailed log was found at this path :

Keep in mind that your appsettings.json file was not deployed

You need to add SqlConnection string in your app with prefix as explained : Configure Connection Strings