Error returning API when running in parallel - C#

Question

Hello,

I’m having doubts as to which solution I could apply to the following problem:

I built an API that when called makes several calls in some databases and after composing and concatenating the data it makes a call to another API to which I am client, passing as parameter the data I obtained at the beginning of the process. The problem is that my API will be called by several users and this causes it to get lost, this is before concluding the first call it is already manipulating data of the second bringing wrong results.

Questions:

1) There is a way to stop the initial API method so that it only starts a new execution if it completes the execution in progress?

2) Or there is how it runs in parallel with other calls of itself receiving different parameters?

Here’s a brief example of the methods I’m trying to run in parallel or sequential.

    public string ChamadaInicialDaAPI(string paramInic)
    {
        string retApi = IniciaProcessoApi(paramInic);
        return retApi;
    }

    private string IniciaProcessoApi(string paramInic)
    {
        lock (this)
        {
            string strPesq1 = “”;
            string retApiExt = “”;

            DAL.ProcessaDados logs = new DAL.ProcessaDados();
            strPesq1 = logs.PesquisaDados(paramInic);

            BLL.EnviaDados sendData = new BLL.EnviaDados();
            retApiExt = sendData.EnviaRequisicaoApiExterna(strPesq1);

            return retApiExt;
        }
    }