Hi @pixelyoursite ,
To fix this issue you can remove the Guzzle dependency and the facebook-php-business-sdk files that use it during the packaging step, since the PixelYourSite plugin does not use any of the SDK files that reference this dependency.
Here is an example of how to fix this error:
https://github.com/facebookincubator/Facebook-Pixel-for-Wordpress/commit/6582b2c56d98c3bf5ce5ccb6d7d151ea1edd7f03
