JWT Token Error in AZURE

Question

ERROR MESSAGE RECEIVED

ArgumentNullException: String reference not set to an instance of a String. (Parameter 's')
System.Text.Encoding.GetBytes(string s)
System.Text.UTF8Encoding+UTF8EncodingSealed.GetBytes(string s)
API.Extensions.IdentityServiceExtensions+<>c__DisplayClass0_0.<AddIdentityServices>b__0(JwtBearerOptions options) in IdentityServiceExtensions.cs
Microsoft.Extensions.Options.ConfigureNamedOptions<TOptions>.Configure(string name, TOptions options)
Microsoft.Extensions.Options.OptionsFactory<TOptions>.Create(string name)
Microsoft.Extensions.Options.OptionsMonitor<TOptions>+<>c__DisplayClass11_0.<Get>b__0()
System.Lazy<T>.ViaFactory(LazyThreadSafetyMode mode)
System.Lazy<T>.ExecutionAndPublication(LazyHelper executionAndPublication, bool useDefaultConstructor)
System.Lazy<T>.CreateValue()
System.Lazy<T>.get_Value()
Microsoft.Extensions.Options.OptionsCache<TOptions>.GetOrAdd(string name, Func<TOptions> createOptions)
Microsoft.Extensions.Options.OptionsMonitor<TOptions>.Get(string name)
Microsoft.AspNetCore.Authentication.AuthenticationHandler<TOptions>.InitializeAsync(AuthenticationScheme scheme, HttpContext context)
Microsoft.AspNetCore.Authentication.AuthenticationHandlerProvider.GetHandlerAsync(HttpContext context, string authenticationScheme)
Microsoft.AspNetCore.Authentication.AuthenticationService.AuthenticateAsync(HttpContext context, string scheme)
Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
DevExpress.AspNetCore.Internal.BinaryStorageMiddleware.Invoke(HttpContext httpContext)
DevExpress.AspNetCore.Internal.ResourceManagerMiddleware.Invoke(HttpContext httpContext)
Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

This error is coming from this class

public static class IdentityServiceExtensions
    {
        public static IServiceCollection AddIdentityServices(this IServiceCollection services,
            IConfiguration config)
        {
            var builder = services.AddIdentityCore<AppUser>();

            builder = new IdentityBuilder(builder.UserType, builder.Services);
            builder.AddEntityFrameworkStores<MultiChaxContext>();
            builder.AddSignInManager<SignInManager<AppUser>>();

            services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
                .AddJwtBearer(options =>
                {
                    options.TokenValidationParameters = new TokenValidationParameters
                    {
                        ValidateIssuerSigningKey = true,
                        IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(config["Token:Key"])),
                        ValidIssuer = config["Token:Issuer"],
                        ValidateIssuer = true,
                        ValidateAudience = false
                    };
                });

            return services;
        }
    }

Just by reading the exception message, I can tell that the TOKEN KEY is null but here's my appSetting.json for your reference

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "ConnectionStrings": {
    "DefaultConnection": "My connection string here"
  },
  "Token": {
    "Key": "super secret key",
    "Issuer": "https://localhost:5001/"
  },
  "AllowedHosts": "*"
}

As you can see, there is a token key in the json file.
To add to that, the website works locally but after being deployed in azure, it doesn't and i received the error above.

Thanks for the help.