Вынес подключения в отдельный класс

Payments/Payment.WebApi/Extensions/AppServicesExtension.cs

+using Microsoft.EntityFrameworkCore;
+using Payment.WebApi.Infrastructures.Databases;
+using Payment.WebApi.Repositories;
+using Payment.WebApi.Repositories.Interfaces;
+
+namespace Payment.WebApi.Extensions;
+
+public static class AppServicesExtension
+{
+    public static void AddAppServices(this IServiceCollection services, IConfiguration configuration)
+    {
+        services.AddDbContext<PaymentDbContext>(opt
+            => opt.UseNpgsql(configuration.GetConnectionString("ConnectionString")));
+        services.AddScoped<IUserRepository, UserRepository>();
+        services.AddScoped<ISupplierRepository, SupplierRepository>();
+    }
+}
\ No newline at end of file