Can anyone help... my customer is getting a 'Temporarily Unavailable' message when trying to pay an invoice. Would anyone know a fix?

It's essential to a business to make sure your customer can pay their invoice smoothly, Shauna. I'm here to provide recommendations that you can use.

To start, may I know what payment method your customer is using? This information is helpful so I can check if the Temporarily Unavailable message is related to this. In the meantime, you may advise them to use another payment method. 

If that's not the case, we can let them use an incognito window to pay the invoice. This is to verify if the message is caused by a browser-related issue. Also, the private mode doesn't store cache files that can be damaged and result in odd behaviors when accessing QuickBooks sites. When ready, refer to the following shortcut keys that you can use:

• Google Chrome: press Ctrl + Shift + N
• Mozilla Firefox: press Ctrl + Shift + P
• Microsoft Edge: press Ctrl + Shift + N
• Safari: press Command + Shift +N

Once opened, let them access the pay invoice link again and process the payment. If this works, advise them to go back to their regular browser and clear the cache to eliminate piled-up data that may caused the message. If the same thing happens, I recommend accessing other supported browsers or devices. It might be that the current one their using has a temporary issue with the program.

However, if none of the recommendations works, I suggest reaching out to our phone support team to further investigate the issue. 

If there's anything you want to know about processing invoice payments, please don't hesitate to leave a reply below. I'll be here ready to lend a hand. Have a good day ahead.