c# - Service can't reach post function

Hey (1st time posting here so I may break some rules, tell me if I do),

I'm trying to create a Rest API and I have some problems with.
In fact, the post function is not triggered on the C# API and I don't know why while the GET function used with a getAll() function is running good.

Angular Service :

public GetAll = (): Observable => {
        return this.http.get(this.actionUrl, '').map((response: Response) => response.json());
}
public Add = (thingToAdd: Expertise): Observable => {
    thingToAdd.Id = 1;
    let toAdd = JSON.stringify(thingToAdd);
    console.log(toAdd);
    console.log(this.actionUrl);
    return this.http.post(this.actionUrl, toAdd, { headers: this.headers
}).map((response: Response) => response.json());
}

C# API :

// GET api/values
    [HttpGet]
    public async Task> Get()
    {
        try
        {
            System.Console.WriteLine("Test get all");
            //var result = await cvService.Get("toto@azeo.com");
            return new List();
        }
        catch (System.Exception ex)
        {
            logger.LogError(ex.Message, ex);
            throw;
        }
    }
// POST api/values
    [HttpPost]
    public Expertise Post([FromBody]Expertise expertise)
    {
        try
        {
            System.Console.WriteLine("Test post");
            context.Expertises.Add(expertise);
            context.SaveChanges();
        logger.LogInformation("New expertise added !");
        return expertise;
        }
        catch (System.Exception ex)
        {
            logger.LogError(ex.Message, ex);
            throw;
        }
    }

Expertise (EF model) :

public class Expertise
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public ICollection CVs { get; set; }
}

If anyone has an idea to "link" the service and my API tell me, I'm stuck on it for a since a long time.

Thank you in advance