Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'connectionString') after Upgrading .NET 5 to .NET 7

I have upgraded my API to be working with .NET 7 and Ubuntu 23.04, everything went fine, the API and database are connected on my local machine and I can send request, but when I publish and deploy the app to my server, it seems that it doesn't read the connectionString in appsetting.json .

Here is my appsettings.json

{
    "AppSettings": {
        "Secret": "*************",
        "EmailFrom": "********",
        "SmtpHost": "v******",
        "SmtpPort": 587,
        "SmtpUser": "a*****",
        "SmtpPass": "HJu******"
    },

  "ConnectionStrings": {
    "WebApiDatabase": "Data Source=WebApiDatabase.db",
    "HangfireConnection": "Server=**.**.***.***;Port=5432;Database=Min;User Id=postgres;Password=min***;" //server
    //"HangfireConnection": "Host=localhost;Port=5432;Database=Min;User Id=postgres;Password=*****;" // local
  },

    "Logging": {
      "LogLevel": {
        "Default": "Information",
        "Microsoft": "Warning",
        "Microsoft.Hosting.Lifetime": "Information",
        "Hangfire": "Information"
      } 
    },

    "AllowedHosts": "*",

  "postgresqlconnection": {
    "connectionString": "Server=**.**.***.***;Port=5432;Database=Min;User Id=postgres;Password=min***;" //server
    //"connectionString": "Host=localhost;Port=5432;Database=Min;User Id=postgres;Password=*****;" // local
  },

    "mongoconnection": {
        "connectionString": "mongodb://localhost:27017/?readPreference=primary&appname=MongoDB%20Compass%20Community&ssl=false",
        "database": "backlog",
        "collection": "rawData",
        "collectionpMedian": "resultPmedian",
        "collectionClustering": "resultClustering"
    },

    "urlSettings": {
        "staticPageUrl": "http://**.**.***.***",
        "backendUrl": "http://**.**.***.***"
    },

    "variousSettings": {
        "defaultMessage": "A default message if nothing is found in the database."
    }
}

My startup.cs

services.AddHangfire(configuration => configuration
                .SetDataCompatibilityLevel(CompatibilityLevel.Version_170)
                .UseSimpleAssemblyNameTypeSerializer()
                .UseRecommendedSerializerSettings()
                .UsePostgreSqlStorage(Configuration.GetConnectionString("HangfireConnection")));

My DataContext.cs

private readonly IConfiguration Configuration;

        public DataContext(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        protected override void OnConfiguring(DbContextOptionsBuilder options)
        {
            // connect to postgress database
            var connectionString = Configuration["postgresqlconnection:connectionString"];

            options.UseNpgsql(connectionString);
        }

The error

root@ubuntu-4gb:/# /usr/bin/dotnet /var/www/MinAPI/MinWebApi.dll
Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'connectionString')
   at Hangfire.PostgreSql.PostgreSqlStorage..ctor(String connectionString, Action`1 connectionSetup, PostgreSqlStorageOptions options)
   at Hangfire.PostgreSql.PostgreSqlBootstrapperConfigurationExtensions.UsePostgreSqlStorage(IGlobalConfiguration configuration, String connectionString, Action`1 connectionSetup, PostgreSqlStorageOptions options)
   at Hangfire.PostgreSql.PostgreSqlBootstrapperConfigurationExtensions.UsePostgreSqlStorage(IGlobalConfiguration configuration, String connectionString)
   at WebApi.Startup.<ConfigureServices>b__4_2(IGlobalConfiguration configuration) in D:\C Sharp\Startup.cs:line 46
   at Hangfire.HangfireServiceCollectionExtensions.<>c__DisplayClass0_0.<AddHangfire>b__0(IServiceProvider provider, IGlobalConfiguration config)
   at Hangfire.HangfireServiceCollectionExtensions.<>c__DisplayClass1_0.<AddHangfire>b__14(IServiceProvider serviceProvider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(Type serviceType)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Hangfire.HangfireServiceCollectionExtensions.ThrowIfNotConfigured(IServiceProvider serviceProvider)
   at Hangfire.HangfireServiceCollectionExtensions.CreateBackgroundJobServerHostedService(IServiceProvider provider, JobStorage storage, IEnumerable`1 additionalProcesses, BackgroundJobServerOptions options)
   at Hangfire.HangfireServiceCollectionExtensions.<>c__DisplayClass9_0.<AddHangfireServerInner>b__0(IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitDisposeCache(ServiceCallSite transientCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitNoCache(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass2_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
   at WebApi.Program.Main(String[] args) in D:\C Sharp\Program.cs:line 12

I have tried to hardcode the string inside the functions but the same error happens, tried to change variable name the same, tried to update the appsettings.Development.json to be the same as appsetting.json, it worked but when I restart the app service the error appears again.

Please guide me.

Can you please verify that your Appsettings file is actually being published?
Also Appsettings.Development.Json is only read when running locally in an IDE(Visual Studios, ETC). Otherwise it will try and read Appsettings.Json or Appsettings.Production.Json

The error kept appearing every time I update the API on the server, however I found that editing the appsettings.json within the server solves the problem for that time only, and I need to do that every time, however, It can be ignored as the API works perfeclty fine.