Postman is not configured and Permission Issue

I have configured the Postman settings as per the guidelines. However, I see the followning message on the plugin dashboard:

1.You have configured OAuth 2.0 authentication, but have not received permission to use it. Grant permission with Google.

2. Postman is not configured and is mimicking out-of-the-box WordPress email delivery.

I am using PHP 7.4 and my hosting provider has confirmed that the outbound connections are not disabled for this version

RESULT OF CONNECTIVITY TEST

Summary:
Port 443 can be used with the Gmail API.
Port 443 can be used with the SendGrid API.
Port 25 can be used for SMTP to smtp.gmail.com.
Port 443 can be used with the Mandrill API.
Port 443 can be used with the Mailgun API.
No outbound route between this site and the Internet on Port 465.
No outbound route between this site and the Internet on Port 587.

HERE IS THE DIAGNOSTIC TEST

Mailer: postsmtp
HostName: adstardigital.com
cURL Version: 7.74.0
OpenSSL Version: OpenSSL/1.1.1i
OS: Linux host.cts2040.com 3.10.0-1062.12.1.vz7.131.10 #1 SMP Mon Mar 16 15:39:59 MSK 2020 x86_64
PHP: Linux 7.4.13 C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 5.6 en_GB UTF-8
WordPress Theme: Kadence
WordPress Plugins: Akismet Anti-Spam, All In One WP Security, BackWPup, Cookie Notice, Kadence Blocks – PRO Extension, Kadence Blocks – Gutenberg Blocks for Page Builder Features, Kadence Custom Fonts, Kadence Pro – Premium addon for the Kadence Theme, Kadence Starter Templates, Post SMTP, ShortPixel Image Optimizer, SEOPress
WordPress wp_mail Owner: /home/adstar/public_html/wp-content/plugins/post-smtp/Postman/PostmanWpMailBinder.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, PostsmtpMailer->get_mail_args
WordPress phpmailer_init Action(s): PostsmtpMailer->phpmailer_smtp_init
Postman: 2.0.16
Postman Sender Domain (Envelope|Message): adstardigital.com | adstardigital.com
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: Default (smtp:none:none://localhost:25)
Postman Active Transport Status (Ready|Connected): No | Yes
Postman Selected Transport: SMTP (smtp:tls:oauth2://smtp.gmail.com:25)
Postman Selected Transport Status (Ready|Connected): No | Yes
Postman Deliveries (Success|Fail): 1 | 0