Why this codeigniter function parameter isn't working as it should be?

Question

I'm trying to create callback script for Coinbase bitcoin payments. Here is the below function from my payment controller. But somehow the key isn't working as it should. I am trying to access it like that: http://www.example.com/payments/callback?key=true but it's not getting affected basically not working. Take a note that the script is working itself but after adding the key function and validating it ... it's not anymore. The issue is caused by that but I don't know what exactly, so what may cause that in the script below? Thanks for taking the time to check and possibly answer my question.

function is_valid_key($key) {
    // logic to check key
    $valid = true;
    if($valid) {
        return true;
    }
    else {
       return false;
    }
}    

function callback()
    {
        //Check if key is valid.

        $key = $this->input->get('key');
        if( ! $this->is_valid_key($key)) {

        //If key above is valid order is "completed", please proceed.

        $data = json_decode(file_get_contents('php://input'), TRUE);

        $status = $data['order']['status'];
        $userid = '507';

        if (($status === 'completed')) {
            $this->db->query( 'update users set user_money=user_money+15, user_credits=user_credits+5 WHERE users_id=' . $userid );
        }
    }
    }

Answer 1

it has to do with your configuration settings. check out this question Enabling $_GET in codeigniter

Also you can use

parse_str($_SERVER['QUERY_STRING'], $_GET);

which would push GET right back on