Module.EventRegistration/Client/Startup/ClientStartup.cs

using Microsoft.Extensions.DependencyInjection;
using Oqtane.Services;
using System.Linq;
using SZUAbsolventenverein.Module.EventRegistration.Services;

namespace SZUAbsolventenverein.Module.EventRegistration.Startup
{
    public class ClientStartup : IClientStartup
    {
        public void ConfigureServices(IServiceCollection services)
        {
            if (!services.Any(s => s.ServiceType == typeof(IEventRegistrationService)))
            {
                services.AddScoped<IEventRegistrationService, EventRegistrationService>();
            }
        }
    }
}