hi, I can help you to fix this issue real quick. You can drop me a message with admin login at firstname.lastname@example.org
I would uninstall one at a time to be honest. I assume you want to have the same pop-up happen when they click proceed to checkout as when they add a product to the site correct?
it is not actually a native coding issue I don't believe.... but as David stated it may be able to be fixed quickly if you don't want the pop-up to happen.
I have excellent skills for the requirement you asked for. I will assist you at Minimum rates.
You can add me on Skype - seth.cis for project disucssion. You can also contact me via email - email@example.com.
Please check your email for detail how can be helped.
Similar type of work I have done in past, so can help you with your current requirement.
let me know your available time and I will do my best to accommodate it
Skype - anaisys.technologies