How to return to the main page after making a payment on PayBox, with VAADI

Main page: http://localhost:8080/app0
I would like to return to my main page after making a payment. I have a “retour” parameter in my url that is zero until I went to the payment site and I did not validate my payment. After payment, therefore “retour” parameter is non-zero(ex: http://localhost:8080/app0/#!retour?retour=APP:337:2:/QSYS.LIB/CMT31.LIB/PAMWTRCL8.PGM&mt=3000&code=00000&key=krE0CVCuH%2FQ1fw2iOEIt6xYVqdmcUjiUNg2n9oSHcL2UkaE7N5WyzargWQS85u7IKNH6m38zuN3qXcx42KqEfXIiem1MHyfdQdamqzKfCP25Jwze7PPhGBjXSzO4JkKi2Pp2w573XKAwBFMkuaLcBeFb3Uq1qvWyRumYdk89Sro%3D), I would like to return to my main page. My problem is that this parameter is not zero, so I can not go back to the main page. My solution would be to use the fragments but I do not know how to do it. Could you help me.

protected void init(VaadinRequest vaadinRequest) {
    String retour=(String) vaadinRequest.getParameter("retour");
    if(retour!=null) {
        String mt=(String) vaadinRequest.getParameter("mt");
        String code=(String) vaadinRequest.getParameter("code");
        String key=(String) vaadinRequest.getParameter("key");
        traiteRetourPaiement(retour, mt, code, key);
    } else {
        String nomApp = getNomApp(vaadinRequest);
        setContent(new DynamicView(nomApp));