How to use PostAsync() Request in a Loop?

Question

I need send a POST for each object on a List<>.

This is the main function that sends the post

public async Task<string> Set(int pessoaId)
{
    try
    {
        Pessoas pessoa = new PessoasBLL().SelectBy("PessoaID", pessoaId);
        List<Endereco> lstEndereco = new EnderecoBLL().SelectByEntidade(pessoaId);
        Person person = new Person();

        person = SerializePerson(person, pessoa, lstEndereco);


        string token = new IntegracaoBLL().Select().ToUpper();
        // Put the following code where you want to initialize the class
        // It can be the static constructor or a one-time initializer
        if (client.BaseAddress == null)
        {
            client.BaseAddress = new Uri(baseURL);
        }
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(
            new MediaTypeWithQualityHeaderValue("application/json"));
        client.DefaultRequestHeaders.Authorization =
            new AuthenticationHeaderValue("Basic", token);

        var data = JsonConvert.SerializeObject(person);

        var request = new StringContent(JsonConvert.SerializeObject(person), Encoding.UTF8, "application/json");

        var postResponse = await client.PostAsync("person", request);

        if (postResponse.StatusCode == HttpStatusCode.Created || postResponse.StatusCode == HttpStatusCode.NotAcceptable)
        {
            new PessoasBLL().SetImportacao(pessoaId, true);
        }

        return null;
    }
    catch (Exception ex)
    {
        return null;
    }
}

The function work as fine when not in a loop, like this for example:

private void btnTeste_Click(object sender, EventArgs e)
{
    new IntegrationWebApi().Set(8).ConfigureAwait(true);             
}

But I'm having trouble getting this 'code' to work in a loop, like this for example

private void btnTeste_Click(object sender, EventArgs e)
{
    try
    {
        List<Pessoas> pessoas = new PessoasBLL().SelectAllIntegracao();
        foreach (Pessoas p in pessoas)
        {
            new IntegrationWebApi().Set(p.ID).ConfigureAwait(true);
        }
    }
    catch (Exception ex)
    {
        XtraMessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Information);
        new Logger().LogEntry(ex);
    }
}