Fatal error: Class 'GuzzleHttp\Handler\Proxy' not found

[Starystars67]

Hi guys, as the title suggests I am getting the error Fatal error: Class 'GuzzleHttp\Handler\Proxy' not found. Here is a screenshot of the full error:

Does anyone have any ideas how to resolve this?
Here is my file/folder structure:

As im sure you can tell, the rest of the system is loading just fine except this.
Any help much appreciated.

I do not have access to composer unfortunately so that is not an option for any suggestions.