MediatR Nuget package versions creating problems

I am getting a version mismatch error when using MediatR in my .NET project.

What happened:

• Yesterday my project worked correctly with no errors.
• Today I updated some NuGet packages by mistake.
• After that, I tried MediatR 10.0.0 → too many breaking changes.
• Then I tried MediatR 8.0.1 → also incompatible.
• Whatever version I install, I get interface or extension method errors.

My code:

Program.cs:

using udemycarbook.Application.Features.CQRS.Handlers.AboutHandlers;
using udemycarbook.Persistence.Context;
using udemycarbook.Application.Interfaces;
using udemycarbook.Persistence.Repositories;
using udemycarbook.Application.Features.CQRS.Handlers.BannerHandlers;
using udemycarbook.Application.Features.CQRS.Handlers.BrandHandlers;
using udemycarbook.Application.Features.CQRS.Handlers.CarHandlers;
using udemycarbook.Application.Interfaces.CarInterfaces;
using udemycarbook.Persistence.Repositories.CarRepository;
using udemycarbook.Application.Features.CQRS.Handlers.CategoryHandlers;
using udemycarbook.Application.Features.CQRS.Handlers.ContactHandlers;
using udemycarbook.Application.Services;
using UdemyCarBook.Application.Features.CQRS.Handlers.CarHandlers;


var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddScoped<CarBookContext>();
builder.Services.AddScoped(typeof (IRepository<>), typeof(Repository<>));
builder.Services.AddScoped(typeof (ICarRepository), typeof(CarRepository));

builder.Services.AddScoped<GetAboutQueryHandler>();
builder.Services.AddScoped<GetAboutByIdQueryHandler>();
builder.Services.AddScoped<CreateAboutCommandHandler>();
builder.Services.AddScoped<UpdateAboutCommandHandler>(); 
builder.Services.AddScoped<RemoveAboutCommandHandler>();

builder.Services.AddScoped<GetBannerQueryHandler>();
builder.Services.AddScoped<GetBannerByIdQueryHandler>();
builder.Services.AddScoped<CreateBannerCommandHandler>();
builder.Services.AddScoped<UpdateBannerCommandHandler>();
builder.Services.AddScoped<RemoveBannerCommandHandler>();

builder.Services.AddScoped<GetBrandQueryHandler>();
builder.Services.AddScoped<GetBrandByIdQueryHandler>();
builder.Services.AddScoped<CreateBrandCommandHandler>();
builder.Services.AddScoped<UpdateBrandCommandHandler>();
builder.Services.AddScoped<RemoveBrandCommandHandler>();

builder.Services.AddScoped<GetCarQueryHandler>();
builder.Services.AddScoped<GetCarByIdQueryHandler>();
builder.Services.AddScoped<CreateCarCommandHandler>();
builder.Services.AddScoped<UpdateCarCommandHandler>();
builder.Services.AddScoped<RemoveCarCommandHandler>();
builder.Services.AddScoped<GetCarWithBrandQueryHandler>();
builder.Services.AddScoped<GetLast5CarsWithBrandQueryHandler>();

builder.Services.AddScoped<GetCategoryQueryHandler>();
builder.Services.AddScoped<GetCategoryByIdQueryHandler>();
builder.Services.AddScoped<CreateCategoryCommandHandler>();
builder.Services.AddScoped<UpdateCategoryCommandHandler>();
builder.Services.AddScoped<RemoveCategoryCommandHandler>();

builder.Services.AddScoped<GetContactQueryHandler>();
builder.Services.AddScoped<GetContactByIdQueryHandler>();
builder.Services.AddScoped<CreateContactCommandHandler>();
builder.Services.AddScoped<UpdateContactCommandHandler>();
builder.Services.AddScoped<RemoveContactCommandHandler>();

builder.Services.AddApplicationService(builder.Configuration);



builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();

CreateFeatureCommand:

using MediatR;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace udemycarbook.Application.Features.Mediator.Commands.FeatureCommands
{
    public class CreateFeatureCommand : IRequest
    {
        public string Description { get; set; }
        public string Address { get; set; }
        public string Phone { get; set; }
        public string Email { get; set; }
        public string Name { get;  set; }
    }
}

CreateFeatureCommandHandler:

using MediatR;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using udemycarbook.Application.Features.Mediator.Commands.FeatureCommands;
using udemycarbook.Application.Interfaces;
using UdemyCarBookDomain.Entities;


namespace udemycarbook.Application.Features.Mediator.Handlers.FeatureHandlers
{
    public class CreateFeatureCommandHandler : IRequestHandler<CreateFeatureCommand>
    {
        private readonly IRepository<Feature> _repository;

        public CreateFeatureCommandHandler(IRepository<Feature> repository)
        {
            _repository = repository;
        }

        public async Task Handle(CreateFeatureCommand request, CancellationToken cancellationToken)
        {
            await _repository.CreateAsync(new Feature
            {
                Name = request.Name
            });

        }

        Task<Unit> IRequestHandler<CreateFeatureCommand, Unit>.Handle(CreateFeatureCommand request, CancellationToken cancellationToken)
        {
            throw new NotImplementedException();
        }
    }
}

Errors I get:

Inside of image i add, but right now i fixed those errors by adding this

Task<Unit> IRequestHandler<CreateFeatureCommand, Unit>.Handle(CreateFeatureCommand request, CancellationToken cancellationToken)
{
    throw new NotImplementedException();
}

to each of them, for now i get this

'MediatRServiceConfiguration' does not contain a definition for 'RegisterServicesFromAssembly' and no accessible extension method 'RegisterServicesFromAssembly' accepting a first argument of type 'MediatRServiceConfiguration' could be found (are you missing a using directive or an assembly reference?)

and this

Metadata file "'C:\Users\yunus\source\repos\udemycarbook\Core\udemycarbook.Application\obj\Debug\net8.0\ref\udemycarbook.Application.dll' could not be found"

I want to know:

• Which MediatR version matches my code syntax?
• How should I correctly register MediatR in Program.cs?

you can see my errors in here, it's saying that i need to add somethings but just a day ago it wasn't necessary.