My client gets an error message when tries to pay with his credit card it says !Error You can try again or come back later and try connecting then

Hi alunahomestaging,

Welcome to the QuickBooks Online community family! It sounds like you could be referring to a client in your QuickBooks Online Accountant trying to pay for his subscription or a client attempting to pay an invoice sent through QuickBooks Payments. I'd be happy to address both of these so you can quickly get back on track. 

Because there's no reported issue in QuickBooks Online Accountant and QuickBooks Online Payments for the error you've described, it could be a browser issue causing this problem. To eliminate any probability of a browser issue and to ensure the app or browser used is running the program as designed, I recommend following the troubleshooting steps in this article: Clear cache and cookies to fix issues when using QuickBooks Online

Another good troubleshooting step to resolve these kinds of errors is to navigate in a private/incognito window or use a different browser compatible with QuickBooks Online. Here's an article with the list of supported browsers: System requirements for QuickBooks Online, Accountant, and QuickBooks Self-Employed

I hope this helps! Don't hesitate to reach out if you have more questions.