MS Project Server REST api from SharePoint-Hosted app

I'm trying to get some project data using the REST API. My queries work fine when using Postman. But when it comes to SharePoint-Hosted app, I'm getting a "404 (Not Found)" error. My app is deployed on the PWA root web. Here is my code:

function GetProject() {

        var deferred = $.Deferred();

        JSRequest.EnsureSetup();

        var hostweburl = decodeURIComponent(JSRequest.QueryString["SPHostUrl"]);
        var appweburl = decodeURIComponent(JSRequest.QueryString["SPAppWebUrl"]);

        var context = new SP.ClientContext(appweburl);
        var appContextSite = new SP.AppContextSite(context, hostweburl);

        var restQueryUrl = appweburl + "/_api/SP.AppContextSite(@target)/ProjectServer/Projects?@target='" + hostweburl + "'";

        var executor = new SP.RequestExecutor(appweburl);
        executor.executeAsync({
            url: encodeURI(restQueryUrl),
            method: "GET",
            headers: { "Accept": "application/json; odata=verbose" },
            success: function (data, textStatus, xhr) {
                deferred.resolve(JSON.parse(data.body).d);
            },
            error: function (xhr, textStatus, errorThrown) {
                deferred.reject(JSON.parse(xhr.body).error.message.value);
            }
        });
        return deferred;
};

Would you have some inputs to solve my problem? Thanks.

Regard,