PayPal error upon checkout

Some users of the EShop is experiencing issues when they try to checkout using PayPal.
Only some users...
I have attached the image.
 

Grateful for any advice that could help with the troubleshooting.

Hello bumble,

Thank you for submitting the topic here. I think the reason because you didn't setup PayPal payment plugin properly. Please go to our ticket system at joomdonation.com/support-tickets.html to submit a new ticket to send me the super admin account to your site so I can help you to check and tell you the reason.

Sincerely, Giang