My Client is recieving an error while trying to pay Credit Card through quickbooks

Hello matt-prettyriver,

Thanks for reaching out to us here. It's vital your client is able to pay using a credit card without getting an error message. QuickBooks is designed to help you streamline your work and I'd like to help make sure you experience that. 

Based on the details you've provided, I recommend having your client clear  cache and cookies on their browser. Clearing cache and cookies helps fix most issues the site may be having. Here's an article that shows you how to do that: How to clear cache and cookies. Give this a try and let me know what happens. In case they get the same error again, I recommend contacting our support team so they can investigate the type of error your client is getting and assist with fixing it. 

 Here are our contact details:

• Schedule a Callback or start a Chat: click (?)Help in the upper right in QuickBooks Online > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat.
• Social Media: Facebook, Twitter, and Instagram.
• Support hours are from Monday to Friday between 9 a.m. and 8 p.m. ET.

Feel free to keep me posted on how you make out. I'll be one message away in case you need anything else.