When i try to run the app i get:

System.AggregateException: 'Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: ProductManager.Core.ServiceContracts.IProductAdderService Lifetime: Scoped ImplementationType: ProductManager.Core.Services.ProductAdderService': Unable to resolve service for type 'ProductManager.Core.Domain.RepositoryContracts.IProductRepository' while attempting to activate 'ProductManager.Core.Services.ProductAdderService'.)'

the service interface:

using ProductManager.Core.DTO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ProductManager.Core.ServiceContracts
{
    public interface IProductAdderService
    {
        Task<ProductAddResponse> AddProduct(ProductAddRequest? productAddRequest);
    }
}

the service:

using ProductManager.Core.Domain.Entities;
using ProductManager.Core.Domain.RepositoryContracts;
using ProductManager.Core.DTO;
using ProductManager.Core.ServiceContracts;
using System;
using System.Collections.Generic;
using System.Diagnostics.Metrics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ProductManager.Core.Services
{
    public class ProductAdderService : IProductAdderService
    {
        // private field
        private readonly IProductRepository _productRepository;
        // constructor
        public ProductAdderService(IProductRepository productRepository) {
        _productRepository = productRepository;
        }
        // method
        public async Task<ProductAddResponse> AddProduct(ProductAddRequest? productAddRequest)
        {
            if (productAddRequest == null)
            {
                throw new ArgumentNullException(nameof(productAddRequest));
            }

          /*  //Validation: CountryName can't be null
            if (productAddRequest.CountryName == null)
            {
                throw new ArgumentException(nameof(productAddRequest.CountryName));
            }*/

            //Validation: CountryName can't be duplicate
           /* if (await _countriesRepository.GetCountryByCountryName(countryAddRequest.CountryName) != null)
            {
                throw new ArgumentException("Given country name already exists");
            }*/

            //Convert object from CountryAddRequest to Country type
            Product product = productAddRequest.ToProduct();

            //generate CountryID
            product.ProductId = Guid.NewGuid();

            //Add country object into _countries
            await _productRepository.AddPerson(product);

            return product.ToProductResponse();


        }
    }
}

they are inside the .Core class library;
Then inside the .Infrastructure folder i have repository:

using ProductManager.Core.Domain.Entities;
using ProductManager.Core.Domain.RepositoryContracts;
using ProductsManager.Infrastructure;
using System;
using System.Collections.Generic;
using System.Diagnostics.Metrics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace UserManager.Infrastructure.Repositories
{
    internal class ProductRepository : IProductRepository
    {
        // db context
        private readonly EntityDbContext _db;
        
        // constructor 
        public ProductRepository(EntityDbContext db)
        {
            _db = db;
        }

        // methods

        public async Task<Product> AddPerson(Product product)
        {
            _db.Products.Add(product);
            await _db.SaveChangesAsync();
            return product;
        }

        public Task<List<Product>> GetAllProducts()
        {
            throw new NotImplementedException();
        }

        public Task<Product?> GetCountryByProductID(Guid productID)
        {
            throw new NotImplementedException();
        }

        public Task<Product?> GetProductByCountryName(string productName)
        {
            throw new NotImplementedException();
        }
    }
}

that implements a interface from .Core library class

using ProductManager.Core.Domain.Entities;
using System;
using System.Collections.Generic;
using System.Diagnostics.Metrics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ProductManager.Core.Domain.RepositoryContracts
{
    public interface IProductRepository
    {
        Task<Product> AddPerson(Product product);
        Task<List<Product>> GetAllProducts();

        Task<Product?> GetCountryByProductID(Guid productID);

        Task<Product?> GetProductByCountryName(string productName);
    }
}

And the program.cs inside the .UI

using Microsoft.EntityFrameworkCore;
using ProductManager.Core.Domain.RepositoryContracts;
using ProductManager.Core.ServiceContracts;
using ProductManager.Core.Services;
using ProductsManager.Infrastructure;

var builder = WebApplication.CreateBuilder(args);



// Adding Entity Framework
builder.Services.AddDbContext<EntityDbContext>(options => {
    options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"));
});
//
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();

I have a project refernce to
from UI to Infrascture and Core
from Infrastructure to Core

I’m following:
https://github.com/Harsha-Global/AspNetCore-Harsha/tree/main/23.%20Clean%20Architecture
and i dont really undestand why i get this error.

In the role project,

there’s no builder.Services.AddScoped...
or there’s no:

builder.Services.AddScoped<IProductRepository, ProductRepository>();
builder.Services.AddScoped<IProductAdderService, ProductAdderService>();

but still works…
so maybe the problem is with DI? Or with project references?