Critical errors

We have recently started receiving critical errors related to this plugin.

Testing email from within the plugin doesn’t work and has critical error posted.

Even just logging into website creates a critical error.

Processing an order in woocommerce produces error.

We are not receiving emails from the website.

Here is a debug log file from test email which shows critical error. Any ideas on how we can resolve this?

[20-May-2026 22:09:07 UTC] PHP Fatal error:  Uncaught Error: Call to undefined function GuzzleHttp\choose_handler() in /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/vendor/guzzlehttp/guzzle/src/HandlerStack.php:40
Stack trace:
#0 /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/vendor/guzzlehttp/guzzle/src/Client.php(65): GuzzleHttp\HandlerStack::create()
#1 /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/src/Google/Client.php(1058): GuzzleHttp\Client->__construct(Array)
#2 /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/src/Google/Client.php(1032): Google_Client->createDefaultHttpClient()
#3 /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/src/Google/Client.php(277): Google_Client->getHttpClient()
#4 /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/src/Google/Client.php(255): Google_Client->fetchAccessTokenWithRefreshToken('1//0fxe0LdJCpwC...')
#5 /home/xxx/public_html/wp-content/plugins/gmail-smtp/class.phpmaileroauthgoogle.php(154): Google_Client->refreshToken('1//0fxe0LdJCpwC...')
#6 /home/xxx/public_html/wp-includes/PHPMailer/SMTP.php(636): GmailXOAuth2->getOauth64()
#7 /home/xxx/public_html/wp-content/plugins/gmail-smtp/class.phpmaileroauth.php(154): PHPMailer\PHPMailer\SMTP->authenticate('', '', 'XOAUTH2', Object(GmailXOAuth2))
#8 /home/xxx/public_html/wp-includes/PHPMailer/PHPMailer.php(2175): PHPMailerOAuth->smtpConnect(Array)
#9 /home/xxx/public_html/wp-includes/PHPMailer/PHPMailer.php(1798): PHPMailer\PHPMailer\PHPMailer->smtpSend('Date: Wed, 20 M...', 'test\r\n')
#10 /home/xxx/public_html/wp-includes/PHPMailer/PHPMailer.php(1615): PHPMailer\PHPMailer\PHPMailer->postSend()
#11 /home/xxx/public_html/wp-content/plugins/gmail-smtp/main.php(1128): PHPMailer\PHPMailer\PHPMailer->send()
#12 /home/xxx/public_html/wp-includes/class-wp-hook.php(341): gmail_smtp_pre_wp_mail(NULL, Array)
#13 /home/xxx/public_html/wp-includes/plugin.php(205): WP_Hook->apply_filters(NULL, Array)
#14 /home/xxx/public_html/wp-includes/pluggable.php(231): apply_filters('pre_wp_mail', NULL, Array)
#15 /home/xxx/public_html/wp-content/plugins/gmail-smtp/main.php(229): wp_mail('patrick@marketi...', 'test', 'test')
#16 /home/xxx/public_html/wp-content/plugins/gmail-smtp/main.php(158): GMAIL_SMTP->test_email_settings()
#17 /home/xxx/public_html/wp-includes/class-wp-hook.php(341): GMAIL_SMTP->options_page('')
#18 /home/xxx/public_html/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters('', Array)
#19 /home/xxx/public_html/wp-includes/plugin.php(522): WP_Hook->do_action(Array)
#20 /home/xxx/public_html/wp-admin/admin.php(264): do_action('settings_page_g...')
#21 /home/xxx/public_html/wp-admin/options-general.php(10): require_once('/home/xxx/p...')
#22 {main}
  thrown in /home/xxx/public_html/wp-content/plugins/gmail-smtp/google-api-php-client/vendor/guzzlehttp/guzzle/src/HandlerStack.php on line 40