This web site can't be reached ASP .NET core web api

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.NET-Core

hello every one i working a project with angular and asp .net core web api

i already have the DB so i did the scaffolding and it generate the models but when i create the controller with entity framwork with actions and i want to test the api i get this :
get : http://localhost:28102/api/Responsables

the result
this web site can't be reached .

i don t know what s the problem .

What I have tried:

My contoller :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using ApiBack.Models;

namespace ApiBack.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class ResponsablesController : ControllerBase
    {
        private readonly gestion_livraisonContext _context;

        public ResponsablesController(gestion_livraisonContext context)
        {
            _context = context;
        }

        // GET: api/Responsables
        [HttpGet]
        public IEnumerable<Responsable> GetResponsable()
        {
            return _context.Responsable;
        }

        // GET: api/Responsables/5
        [HttpGet("{id}")]
        public async Task<IActionResult> GetResponsable([FromRoute] int id)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var responsable = await _context.Responsable.FindAsync(id);

            if (responsable == null)
            {
                return NotFound();
            }

            return Ok(responsable);
        }

        // PUT: api/Responsables/5
        [HttpPut("{id}")]
        public async Task<IActionResult> PutResponsable([FromRoute] int id, [FromBody] Responsable responsable)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != responsable.IdResponsable)
            {
                return BadRequest();
            }

            _context.Entry(responsable).State = EntityState.Modified;

            try
            {
                await _context.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ResponsableExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return NoContent();
        }

        // POST: api/Responsables
        [HttpPost]
        public async Task<IActionResult> PostResponsable([FromBody] Responsable responsable)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            _context.Responsable.Add(responsable);
            await _context.SaveChangesAsync();

            return CreatedAtAction("GetResponsable", new { id = responsable.IdResponsable }, responsable);
        }

        // DELETE: api/Responsables/5
        [HttpDelete("{id}")]
        public async Task<IActionResult> DeleteResponsable([FromRoute] int id)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var responsable = await _context.Responsable.FindAsync(id);
            if (responsable == null)
            {
                return NotFound();
            }

            _context.Responsable.Remove(responsable);
            await _context.SaveChangesAsync();

            return Ok(responsable);
        }

        private bool ResponsableExists(int id)
        {
            return _context.Responsable.Any(e => e.IdResponsable == id);
        }
    }
}

My Model :

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace ApiBack.Models
{
    public partial class Responsable
    {
        public Responsable()
        {
            Agence = new HashSet<Agence>();
        }
        [Key]
        public int IdResponsable { get; set; }
        public string NomResponsable { get; set; }
        public string PrenomResponsable { get; set; }
        public string LoginResponsable { get; set; }
        public string MdpResponsable { get; set; }
        public int? Ville { get; set; }

        public Ville VilleNavigation { get; set; }
        public ICollection<Agence> Agence { get; set; }
    }
}

the dbcontext class:

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata;

namespace ApiBack.Models
{
    public partial class gestion_livraisonContext : DbContext
    {
       

        public gestion_livraisonContext(DbContextOptions options)
            : base(options)
        {
        }

        public virtual DbSet<Agence> Agence { get; set; }
        public virtual DbSet<ClientPar> ClientPar { get; set; }
        public virtual DbSet<ClientPro> ClientPro { get; set; }
        public virtual DbSet<Commande> Commande { get; set; }
        public virtual DbSet<Livreur> Livreur { get; set; }
        public virtual DbSet<Responsable> Responsable { get; set; }
        public virtual DbSet<Superadmin> Superadmin { get; set; }
        public virtual DbSet<Ville> Ville { get; set; }
    }
}