We have passed credit note for last month invoice but it not closed

I know it is important to ensure your transactions are recorded accurately in QuickBooks, arun-kumar-tagbo. I'm here to assist you with that.

Since the transaction isn't closed yet, I'd suggest applying the credit note to the invoice. Here's how:

1. Go to the + New menu and then select Receive payment.
2. In the Customer drop-down menu, select the customer.
3. In the Outstanding Transactions section, select the open invoice you want to apply the credit note to.
4. In the Credits section, select the credit notes you want to apply.
5. For the open invoice in the Payment column, enter how much of the credit you want to apply.
6. Leave the Payment method, Reference no, Deposit to, and Amount received fields blank.
7. Fill out the rest of the form, including the Payment date.
8. Make sure the total is correct after applying the credit note.
9. When you're done, select Save and close.

If you're unable to do so, I'd suggest deleting and recreating the credit note and the invoice. This way, we'll be able to link the transactions. For the detailed steps, please see this article: Create and Apply Credit Notes or Delayed Credits.

In case you'd like to return your customer's money instead of giving credit, I encourage checking out this article: Record a Customer Refund in QuickBooks Online.

I'm only a post away if you need more help in completing your other tasks in QuickBooks, arun-kumar-tagbo.  It's always my pleasure to help you out again.