PHP Post $_Cookie without curl to external site

[Nauj]

Hi,
I am trying to make an application to automate login and registry to a webpage without the user having to do it manually. The secuence should be something like this:

a)--- Response.php (my php code) sends a post login request to 3rd party url
b)--- Third party url sends back login cookie
c)--- Response.php sends new post requesting registration for a class.

The problem I have is, although I retrieve the cookie correctly I can't seem able to send it again on the 2nd interaction and
the 3rd party server always gives me a "Logout" response.

a) + b)

$url = 'https://aimharder.com/login';
$data = array('mail' => 'useremail@gmail.com', 'pw' => 'userpass', 'login' => 'Log In');
$data = http_build_query($data);

$options = array(
  'http' => array(
    'header'  => 'Content-type: application/x-www-form-urlencoded\r\n',
    'method'  => 'POST',
    'content' => $data,
  ),
);

$context  = stream_context_create($options);
$result = file_get_contents($url, false, $context);
print_r ($_COOKIE);
//This works ok

This second part is when the problem begins:

$url = 'https://komcrossfit.aimharder.com/api/book';
$cookie_amhrdrauth = 'Cookie: amhrdrauth=' . $_COOKIE['amhrdrauth'];
$data = array('id' => '9043', 'day' => '20180331', 'insist' => '0');

$data = http_build_query($data);
$header = array ('Content-type: application/x-www-form-urlencoded\r\n' , $cookie_amhrdrauth);

$options = array(
    'http' => array(
    'header'  => $header,
    'method'  => 'POST',
    'content' => $data
  )
);

I have tried many different variations to how to set up $header but none seem to send the cookie to the url and it always gives me a logout resonse.

Please help!!