May be you have to give a try to odoo addon website_livechat. 

when you setup it you get the links, just copy thats and put in your pestrashop site.

Its work with both odoo and pestrashop at a time with same operator.

For me it works perfectly.

Thank You.

Hi I would recommend Click4Assistance, they are the leading UK provider of live chat software and you can add their live chat to any website. We have received very positive from our staff who operate it and our visitors. Simply start a trial at http://www.click4assistance.co.uk and they will send you an email with everything you need to integrate.   

Hi Kevin Lee, 

Check it out here: http://addons.prestashop.com/en/front-office-features-prestashop-modules/5531-live-chat.html

Prestashop is one of the highly popular free ecommerce website in the world that provides a platform where we can successfully build a customizable online store. So, you can integrate suitable chat plugin eAssistance Pro Live Chat Module for Prestashop, that enable you to add a live chat solution on your Prestashop store. It's extremely customizable and compatible chat plugin which can easily install on Prestashop store. For integration https://www.eassistancepro.com/addons/magento.php