Bad Request(invalid_grant) with Gmail in Post SMTP

Hi All,

I have been unable to get Post SMTP working with Gmail API.

The error I get back whenever trying to send an email is

Bad Request(invalid_grant).

Here is my diagnostics

Mailer: postsmtp
HostName: web.geckopico.synology.me
cURL Version: 7.79.1
OpenSSL Version: OpenSSL/1.1.1n
OS: Linux DS920 4.4.180+ #42661 SMP Mon Jun 27 15:07:20 CST 2022 x86_64
PHP: Linux 7.4.28 en_US.UTF-8
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=No, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 5.8.3 en_AU UTF-8
WordPress Theme: Enfold
WordPress Plugins: CC Child Pages, Easy share solution, Post SMTP, SVG Support, Wordfence Assistant, Wordfence Security, Yoast SEO, WP Githuber MD
WordPress wp_mail Owner: /volume1/web/instances/web/wordpress/wp-content/plugins/post-smtp/Postman/PostmanWpMailBinder.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, PostsmtpMailer->get_mail_args
WordPress wp_mail_from Filter(s): wordfence::fixWPMailFromAddress
WordPress phpmailer_init Action(s): PostsmtpMailer->phpmailer_smtp_init
Postman: 2.1.4
Postman Sender Domain (Envelope|Message): gmail.com | gmail.com
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: SMTP (smtp:tls:oauth2://smtp.gmail.com:587)
Postman Active Transport Status (Ready|Connected): Yes | Yes
Postman Deliveries (Success|Fail): 0 | 21

Any ideas on what might cause this?

Thanks

GP