I want to post a comment to google plus post using php google client but I didn't find any documentation for how to do this. Please point me on the right path.
Any help much appreciated.
The Google+ API is read only. You can select from it only you can not use it to post to the Google+ Social media website.
The closes you can come to is Google+ share which basicly just gives you a share button users can use.
<!-- Place this tag in your head or just before your close body tag. -->
<script src="https://apis.google.com/js/platform.js" async defer></script>
<!-- Place this tag where you want the share button to render. -->
<div class="g-plus" data-action="share"></div>