ACS.Users.login API Getting error code 400 with message: 'Invalid request sent.'

Hi All,

I am getting below for while login with ACS APP user Data account. But it not occuring always. It only if I call service multiple time.

error:

{
success: false
error: true
code: 400
message: "Invalid request sent."
}

ACS.Users.login(userData, function(data){
        if(data.success) {
            console.log("----------Successful to login.---------------");
            console.log(data);
            res.send(data);
            res.end();
 
        } else {
            console.log("------------------login failed---------------");
            console.log(data);
            res.send(data);
            res.end();
        }
    },req, res);

What my purpose is to store some data in "custom object". How I can keep session / check session validity before pushing something to custom object?

Thanks

Peter