Problem with the "Login External" extension

[jkbavaria]

I would like to use the "Login External" extension to connect SnappyMail with Joomla.

To test this I have written the following PHP script:

---

$target_url = 'http://192.168.11.5:8888';

$post_data = [
'Email' => 'my@domain.de',
'Password' => '12345'
];

$context = stream_context_create([
'http' => [
'method' => 'POST',
'header' => 'Content-type: application/x-www-form-urlencoded',
'content' => $post_data
],
]);

$response = file_get_contents($target_url, false, $context);
echo $response;

---

Unfortunately, I get the following error message:

An error occurred.
Please refresh the page and try again.
SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

What am I doing wrong?