Guzzle 6 dependency throwing fatal error

Hi, I recently installed this plugin and it is causing my site to crash. According to the error log, there is an undefined constant. This is conflicting with other plugins that use Guzzle 7.

According to this thread, updating to Guzzle 7 will fix this issue.

https://github.com/guzzle/guzzle/issues/2744#issuecomment-716709685