Critical Error effecting Woocommerce ANZ Egate Checkouts

Hey – how’s it going?

After upgrading to WP 5.8 I am getting the following Critical Error reporting in Debug & Woo Logs when trying to checkout using ANZ Egate plugin (https://woocommerce.com/products/anz-egate/)

2021-08-04T00:36:38+00:00 CRITICAL Uncaught Error: Call to undefined function GuzzleHttp\Psr7\stream_for() in /home/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/guzzlehttp/psr7/src/MessageTrait.php:126
Stack trace:
#0 /home/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/google/apiclient/src/Google/Http/MediaFileUpload.php(219): GuzzleHttp\Psr7\Request->getBody()
#1 /home/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/google/apiclient/src/Google/Http/MediaFileUpload.php(92): Google_Http_MediaFileUpload->process()
#2 /home/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/PostmanGmailApiModuleZendMailTransport.php(210): Google_Http_MediaFileUpload->__construct(Object(Google_Client), Object(GuzzleHttp\Psr7\Request), 'message/rfc822', 'X-Mailer: Postm...', true, 1048576)
#3  in /home/public_html/wp-content/plugins/post-smtp/Postman/Postman-Mail/google-api-client/vendor/guzzlehttp/psr7/src/MessageTrait.php on line 126

When I send a test email I get the “Ajax Error“.

Connectivity test says Service available – No:

Transport	Socket	Status*	Service Available
SMTP	www.googleapis.com:25	Open	No
SMTP	www.googleapis.com:465	Open	No
SMTP	www.googleapis.com:587	Open	No

There are no emails in the logs since July 31, when I upgraded WP. No new plugins have been installed. Everything was working well before the upgrade.

Here is my diagnostics:

Mailer: postsmtp
HostName: entosupplies.com.au
cURL Version: 7.52.1
OpenSSL Version: OpenSSL/1.0.2u
OS: Linux 274030.cloudwaysapps.com 4.9.0-12-amd64 #1 SMP Debian 4.9.210-1 (2020-01-20) x86_64
PHP: Linux 7.3.29-1+0~20210701.86+debian9~1.gbp7ad6eb C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=Yes, mcrypt=No, zlib_encode=Yes
WordPress: 5.8 en_AU UTF-8
WordPress Theme: Australian Entomological Supplies
WordPress Plugins: ManageWP - Worker, Advanced Custom Fields PRO, Automattic Humility, Five Star Business Profile and Schema, Classic Editor, GDPR Cookie Consent, Disable Genesis Schema, Google Tag Manager for WordPress, Genesis Connect for WooCommerce, Genesis Simple FAQ, Gravity Forms, Max Mega Menu, Popup Builder, Post SMTP, reCaptcha for WooCommerce, Relevanssi, Rank Math SEO, Simple Social Icons, User Role Editor, WooCommerce Advanced Bulk Edit, Print Invoice & Delivery Notes for WooCommerce, WooCommerce ANZ eGate Gateway, WooCommerce PayPal Checkout Gateway, WooCommerce Purchase Order Payment Gateway, WooCommerce Australia Post Shipping, WooCommerce Xero Integration, WooCommerce, WP All Export Pro, WP All Import Pro, WP All Import - ACF Add-On, WP All Import - WooCommerce Add-On Pro, YITH WooCommerce Request A Quote Premium
WordPress wp_mail Owner: /home/274030.cloudwaysapps.com/ctcgheafry/public_html/wp-content/plugins/post-smtp/Postman/PostmanWpMailBinder.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email, PostsmtpMailer->get_mail_args
Postman: 2.0.23
Postman Sender Domain (Envelope|Message): entosupplies.com.au | entosupplies.com.au
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Active Transport: Gmail API (https:none://www.googleapis.com:443)
Postman Active Transport Status (Ready|Connected): Yes | Yes
Postman Deliveries (Success|Fail): 15622 | 59

Any ideas?