Guzzle 7 dependency conflict with another WordPress plugin

Hello, I’m experiencing a fatal error in the Gmail SMTP plugin during the Google OAuth authentication process when the Metricool WordPress plugin is active. The error appears to be caused by the version of google-api-php-client bundled with Gmail SMTP, which references: GuzzleHttp\ClientInterface::VERSION This constant was removed in Guzzle 7 and replaced by MAJOR_VERSION . The error points to: google-api-php-client/src/Google/Client.php Disabling Metricool temporarily prevents the error, but this is not a viable long-term solution. I contacted the Metricool support team, and they provided the following diagnosis: Hi @codrx, Thanks for sharing the error message and diagnosis with us. It looks like this error isn’t due to “two Guzzle versions fighting” in the usual sense. Guzzle 7 is loaded (as intended), but the other plugin’s source code is too old and incompatible with it. The fatal error occurs because the Gmail SMTP plugin bundles an outdated Google API PHP client that still references GuzzleHttp\ClientInterface::VERSION . In Guzzle 7 that constant was removed (replaced by MAJOR_VERSION ), so once Metricool has loaded Guzzle 7, the Gmail SMTP code crashes during OAuth. Your error message pointing at google-api-php-client/src/Google/Client.php suggests an old client (v2.5.x or earlier). Current google-api-php-client releases should handle both Guzzle 6 and 7 safely; from v2.6.0 onward the VERSION constant is no longer accessed directly, and recent releases such as v2.15.3+ explicitly support Guzzle 6 and 7 in their dependencies. This is not a bug in Metricool’s Guzzle integration per se, but the Gmail SMTP plugin needs to update its bundled google-api-php-client to avoid this conflict. Disabling Metricool only works because it prevents Guzzle 7 from loading first, which confirms the diagnosis, but I can imagine that it isn’t a viable long-term fix. We do not currently plan to downgrade Guzzle, so we recommend contacting the Gmail SMTP developer with your error log; they should be able to resolve this by updating google-api-php-client . Thanks again for sharing the errors here, hope this helps! Kind regards, Jarno Could you please investigate this issue and update the bundled google-api-php-client library to a version compatible with Guzzle 7? Thank you for your help. Thank you! Hi, Thanks for reporting this issue. What version of PHP are you using? Hello, We are using 8.2 Hello, Any updates regarding this? Thank you! Hi, I’m really sorry. It will take a while to update the library and test the changes. Hello, Thank you very much for the update. Waiting for the release. Thanks! Hi, An update has been released. Let me know how it goes.