What is unexpected user error -10601

Thank you for posting here on the Community, zyx07628. I'll make sure to help you fix this error.

Error 10601 occurs when your QuickBooks Online account is inactive or there are cached data or cookies in the web browser that may cause this error.

Let's verify that your QBO account is active and review your account status by accessing the Subscription and Billing section.

Here's how:

1. Sign in to your QuickBooks Online account as Primary Admin.
2. Select the Gear icon, then Subscriptions and Billing.
3. Check the status if it's inactive, select Re-subscribe, and enter the updated billing info.
4. Follow the on-screen instructions and click Subscribe.

If your account is active, we can perform some troubleshooting steps to fix this. There are times when the browser is full of frequently accessed page resources, which causes some errors or unusual responses. 

Let's start accessing your account using a different or private browser. You can use either of these shortcut keys:

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

If it works, I recommend clearing your browser's cache. Doing so will remove the historical data and access QuickBooks with a clean slate. You can also switch to a different supported browser.

In case you want to personalize your sales forms before sending them to your customer, you can visit this article to learn how: Customize invoices, estimates, and sales receipts in QuickBooks Online. 

If you encounter another error while navigating your QBO account, please make another post. I'll ensure to assist you promptly.