Hello, Steph.

I can share some information about viewing attachments in QuickBooks Online (QBO).

The error you're having upon viewing the attachment can be caused by the piled-up cache in your regular browser. A browser's cache stores temporary internet files from your browsing history. However, as it collects too many files, this may cause performance issues in your account.

Try using a private browser when viewing your attachments. If it works, proceed and clear the cache in the one that you're currently using. This helps isolate the issue since it doesn’t store data in the cache. Here are the following keyboard shortcuts: 

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

If it works, here's how to clear cache and cookies to fix issues when using QuickBooks Online. Restart your browser right after. You can also try to log in to your account using other supported browsers (Firefox, Google Chrome, Safari, Microsoft Edge) if the steps above didn’t work.

Here's more information on how to edit and remove attachments from your invoices or other transactions in QBO: Add or delete attachments in QuickBooks Online. 

I'm always here if you need more help with your invoice attachments, or anything else. Let me know by leaving a reply below. Have a great rest of the day!