Sending AdditionalData from wordpress

Hi, I have a wordpress site and I can send notifications successfully to my mobile device.

I’m using this code to unset the pushurl

<?php
add_filter('onesignal_send_notification', 'onesignal_send_notification_filter', 10, 4);

function onesignal_send_notification_filter($fields, $new_status, $old_status, $post)
{
    /* Goal: We don't want to modify the original $fields array, because we want the original web push notification to go out unmodified. However, we want to send an additional notification to Android and iOS devices with an additionalData property.
    */
    $fields_dup = $fields;
    $fields_dup['isAndroid'] = true;
    $fields_dup['isIos'] = true;
    $fields_dup['isAnyWeb'] = false;
    $fields_dup['isWP'] = false;
    $fields_dup['isAdm'] = false;
    $fields_dup['isChrome'] = false;
    $fields_dup['data'] = array(
        "myappurl" => $fields['url']
    );
    /* Important to unset the URL to prevent opening the browser when the notification is clicked */
    unset($fields_dup['url']);
    /* Send another notification via cURL */
    $ch = curl_init();
    $onesignal_post_url = "https://onesignal.com/api/v1/notifications";
    /* Hopefully OneSignal::get_onesignal_settings(); can be called outside of the plugin */
    $onesignal_wp_settings = OneSignal::get_onesignal_settings();
    $onesignal_auth_key = $onesignal_wp_settings['app_rest_api_key'];
    curl_setopt($ch, CURLOPT_URL, $onesignal_post_url);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
        'Content-Type: application/json',
        'Authorization: Basic ' . $onesignal_auth_key
    ));
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HEADER, true);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields_dup));
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

    // Optional: Turn off host verification if SSL errors for local testing
    // curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);

    /* Optional: cURL settings to help log cURL output response
    curl_setopt($ch, CURLOPT_FAILONERROR, false);
    curl_setopt($ch, CURLOPT_HTTP200ALIASES, array(400));
    curl_setopt($ch, CURLOPT_VERBOSE, true);
    curl_setopt($ch, CURLOPT_STDERR, $out);
    */
    $response = curl_exec($ch);
    /* Optional: Log cURL output response
    fclose($out);
    $debug_output = ob_get_clean();
    $curl_effective_url = curl_getinfo($ch, CURLINFO_EFFECTIVE_URL);
    $curl_http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    $curl_total_time = curl_getinfo($ch, CURLINFO_TOTAL_TIME);
    onesignal_debug('OneSignal API POST Data:', $fields);
    onesignal_debug('OneSignal API URL:', $curl_effective_url);
    onesignal_debug('OneSignal API Response Status Code:', $curl_http_code);
    if ($curl_http_code != 200) {
    onesignal_debug('cURL Request Time:', $curl_total_time, 'seconds');
    onesignal_debug('cURL Error Number:', curl_errno($ch));
    onesignal_debug('cURL Error Description:', curl_error($ch));
    onesignal_debug('cURL Response:', print_r($response, true));
    onesignal_debug('cURL Verbose Log:', $debug_output);
    }

    */
    curl_close($ch);
    return $fields;
}

This works fine and my notification opens up my app but, I want to know how I can include additional data with these values

key = posts, value = post_id eg 253