Hi Mark,
It is a custom solution incorporated into theme files. It is using AWS SDK for PHP as a dependency via Composer. Latest version.
My troubleshooting led me to your plugin and older version of Guzzle. If I deactivate your plugin the code works just fine.
From what I can see you are using 7.3.0 – 2021-03-23 and AWS SDK requires 7.8.1 – 2023-12-03
