Refit API HTTPPost 'Unexpected character encountered while parsing value' from .net Core 3.0 Console app

Question

I have an api endpoint as follows

    [HttpPost("create")]
    [MapToApiVersion("1.0")]
    public async Task<IActionResult> Post(CarDto carDto)
    {
        return Ok(await _carService.CreateCarAsync(carDto));
    }

The Dto below is a shared do in nuget package with contracts

public class CarDto
{
    [JsonProperty(PropertyName = "Id")]
    public string Id { get; set; }

    [JsonProperty(PropertyName = "Colour")]
    public string Colour{ get; set; }
}

My calling code in the Console app

public interface ICarServiceApi
{
    [Post("/Cars/create")]
    Task<bool> CreateCar(CarDto carDto);
}

var carServiceApi = RestService.For<ICarServiceApi>("https://localhost:5001/api/v1");
var car = new CarDto {Id ="123", Colour = "Red"};

await carServiceApi.CreateCar(car);

The exception i get is as follows

Unexpected character encountered while parsing value: {. Path '', line 1, position 1.

The call to the Http get works fine so something is wrong in my setup above