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Collaboration + Fluent SMTP Issue

There is a conflict between Collaboration v1.0.2 and Fluent SMTP v2.2.0 that throws fatal PHP errors when attempting to send emails via SMTP. Disabling the Collaboration plugin resolves the issue.

WordPress  6.0.2
PHP 8.0.12

PHP Fatal error: Uncaught Error: Call to undefined function GuzzleHttp\choose_handler() in /home/

23 responses to “Collaboration + Fluent SMTP Issue”

  1. devusrmk Avatar

    Hello, error is on Fluent form plugin side. Please take a look at the code path:

    PHP Fatal error: Uncaught Error: Call to undefined function GuzzleHttp\choose_handler() in /home/

    — > fluent-smtp <--- /includes/libs/google-api-client/vendor/guzzlehttp/guzzle/src/HandlerStack.php:40

  2. devusrmk Avatar

    Can you please use the latest collaboration version.

    1. Allen Stone Avatar
      Allen Stone

      We are using Collaboration v1.0.2, which is the current version shown in our account.

      1. devusrmk Avatar

        Please share us then wp and ftp login so we can check

  3. devusrmk Avatar

    Removed your comment so it’s not public

  4. devusrmk Avatar

    I am not able to reproduce the error. Enabled Collaboration. Enabled WP Debug and still no fatal error.

    Please take a look at image bellow

    1. Allen Stone Avatar
      Allen Stone

      Go to Settings > Fluent SMTP > Email Test. Open browser console then attempt to send a test email. You’ll see the 500 error login in the browser console. If you enable WP debug logging, it will also record in the log.

  5. devusrmk Avatar

    Thanks a lot for explaining the steps. Will check what can it be and add a patch in the next release.

  6. devusrmk Avatar

    Hello we checked everything from our side and done everything to be compatible. So we raised the ticked on their side as there is some error on their side

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