I appreciate you for letting us know, Roland12. Let me provide troubleshooting steps to help resolve and add file attachments from your bank registers.

In QuickBooks Online, some specific attachment file types are supported by the program to enable uploads to your transactions. To avoid or remedy these errors, make sure your company name in QuickBooks Online only contains accepted characters from this list. You may check this reference for more insights:  Add or delete attachments in QuickBooks Online.

If the issue still persists, you may consider performing troubleshooting steps to help rectify the possibility of a webpage issue. Sometimes a browser is loaded with frequently accessed pages, which results in some unusual behaviors. With this, you'll need to access your account in a private browser to ensure the program runs without storing cache files. You may use these keyboard shortcuts:

• For Google Chrome browser: Ctrl + Shift + N
• For Mozilla Firefox browser: Ctrl + Shift + P
• For Safari browser: Command + Shift + N

If you're able to add the attachment again, you may get back to your default browser and clear its cache or use a different supported browser.

Furthermore, I'm sharing this guide to help you track and review your accounts to make sure they always match your bank and credit card statements: Reconcile an account in QuickBooks Online.

I'll keep this thread available if there's anything else you need further assistance with when adding attachments and managing transactions in your file. Feel free to let me know anytime, and I'll be around to get you covered. Stay safe!