PHP equivalent of Python's oauth2client POST request to Google Reminders

I would like to port this open source Python library for Google Reminders to PHP:

https://github.com/jonahar/google-reminders-cli

I have ported the authorization with the help of https://developers.google.com/identity/protocols/OAuth2WebServer

My PHP version: https://github.com/Jinjinov/google-reminders-php

Now I need to port the Python's oauth2client POST request:

body = {
    '5': 1,  # boolean field: 0 or 1. 0 doesn't work ¯\_(ツ)_/¯
    '6': num_reminders,  # number number of reminders to retrieve
}

HEADERS = {
    'content-type': 'application/json+protobuf',
}

    response, content = self.auth_http.request(
        uri='https://reminders-pa.clients6.google.com/v1internalOP/reminders/list',
        method='POST',
        body=json.dumps(body),
        headers=HEADERS,
    )

My $httpClient POST request returns HTTP 404 - Not Found - even though the Python version is working OK.

authorization is made with https://github.com/googleapis/google-api-php-client

$httpClient is Guzzle Client - http://docs.guzzlephp.org/en/stable/

specifially I used:

• http://docs.guzzlephp.org/en/stable/request-options.html#headers
• http://docs.guzzlephp.org/en/stable/request-options.html#body

My code (full code with authorization and $httpClient is on GitHub):

$HEADERS = [
    'content-type' => 'application/json',
];

function list_reminders($httpClient, $num_reminders) {

    $body = (object)[
        '5' => 1,  // boolean field: 0 or 1. 0 doesn't work ¯\_(ツ)_/¯
        '6' => $num_reminders,  // number of reminders to retrieve
    ];

    $response = $httpClient->request(
        'POST',
        'https://reminders-pa.clients6.google.com/v1internalOP/reminders/list',
        [
            'headers' => $HEADERS,
            'body' => json_encode($body)
        ]
    );
    if ($response->getStatusCode() == $HTTP_OK) {
        $content = $response->getBody();
        $content_dict = json_decode($content);
        if (!array_key_exists('1', $content_dict)) {
            return [];
        }
        $reminders_dict_list = $content_dict['1'];
        $reminders = [];
        foreach($reminders_dict_list as $reminder_dict) {
            array_push($reminders, build_reminder($reminder_dict));
        }
        return $reminders;
    }
    else {
        return null;
    }
}

from PHP equivalent of Python's oauth2client POST request to Google Reminders