When we create invoices so in some cases due to inventory error, inventory goes to negative side, so we need a feature so as to ask for password whenever it goes below 0.

Your idea about having that feature is valuable, Anil, and I'd love to help you submit a request for it in QuickBooks Online (QBO).

As software evolves, it's essential to gather feedback from users like you and submit it directly to our Product Developers team. They will carefully review your suggestions, identify areas that require enhancements, and consider incorporating them into future updates. 

Here's how:

1. Hit the Gear icon at the top, then select Feedback.
2. Type in your product suggestions.
3. Click Next to submit feedback.

You can refer to our Customer Feedback page to track your request.

Meanwhile, you can also set up a reorder point so QuickBooks notifies you whenever your stock Is low. You can refer to the visual process below.

Moreover, you can generate reports to see your sales and inventory status in QuickBooks Online.

I'm still willing to back you up if you need more assistance managing your invoices in QuickBooks Online or any other inventory concerns. I'll keep the thread open so you can comment back.