Returning a http response while continuing a process after closing the connection

return_early.php

<?php

public function sendEarlyResponseHeaders($res)
{
    // Buffer all upcoming output...
    ob_start();

    // Send your response.
    echo json_encode($res);

    // Get the size of the output.
    $size = ob_get_length();

    // Disable compression (in case content length is compressed).
    header("Content-Encoding: none");
    header("Content-Type: application/json");

    // Set the content length of the response.
    header("Content-Length: {$size}");

    // Close the connection.
    header("Connection: close");

    // Flush all output.
    ob_end_flush();
    ob_flush();
    flush();
}

In your controller, you can send the reponse like this:

<?php

$response = ["status" => "recieved", "message" => "You will receieve an email shortly"];
$this->sendEarlyResponseHeaders($response);

// Start sending the email and other processes..
AppEmail::send();