Hi, @huyaohui97. I get your confusions about this sudden charge. I can provide you with two ways to check the reason for your 40-dollar charge last month.
Oftentimes, the charge is cause by an added plan to your QuickBooks subscription.
To confirm this, the first thing you can do is to see your full payment history within your QuickBooks account. There will be a description of the charge that was made for you last month. Here's how:
- Go to the Gear icon.
- Select Subscription and Billing.

- Click on View payment history.

You can also use the tool to look up charges for your product. Feel free to check it up in this article, it is located in the last part: Understand Intuit charges on your credit card or bank statement.
Additionally, if you have multiple accounts, be sure to sign in to the correct account to see the exact details of why you are being charged $40.
Being updated on the payment history of your QuickBooks subscription is essential in tracking your expenditure on the software for business records. Leave a comment below if you need additional assistance.