The input was not valid

Estou recebendo esse erro quando tento executar no postman

{
    "": [
        "The input was not valid."
    ]
}

tentei colocar o attributo FromBody mas o erro permanace:

public async Task<IActionResult> Token([FromBody] LoginModel model)

meu body da requição http:

        {
   "Login":"admin",
   "Password":"123"
}

meu metodo post:

 [HttpPost]
        public async Task<IActionResult> Token([FromBody] LoginModel model)
        {
            if (ModelState.IsValid)
            {
                var result = await _signInManager.PasswordSignInAsync(model.Login, model.Password, true, true);
                if (result.Succeeded)
                {                  
                    var direitos = new[]
                    {
                        new Claim(JwtRegisteredClaimNames.Sub, model.Login),
                        new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString())
                    };

                    var chave = new SymmetricSecurityKey(System.Text.Encoding.UTF8.GetBytes("alura-webapi-authentication-valid"));
                    var credenciais = new SigningCredentials(chave, SecurityAlgorithms.HmacSha256);

                    var token = new JwtSecurityToken(
                        issuer: "Alura.WebApp",
                        audience: "Postman",
                        claims: direitos,
                        signingCredentials: credenciais,
                        expires: DateTime.Now.AddMinutes(30)
                    );

                    var tokenString = new JwtSecurityTokenHandler().WriteToken(token);
                    return Ok(tokenString);//200
                }
                return Unauthorized(); //401
            }
            return BadRequest(); //400
        }