How do I undelete an invoice that i've deleted by mistake?

Hello there, @userruben.

Let's use the audit log to recover the details of your deleted invoice so you can re-enter it in QuickBooks Online (QBO) and keep your data updated.

Once you delete a transaction, like an invoice, you're unable to undelete or restore it in QBO. However, you can recover its details so you can re-enter it into your account. To do this, here's how:

1. Go to the Gear icon.
2. Select Audit log.
3. Choose the appropriate User, Date Changed, and Events from the filter ▼ dropdown menu. 
4. Locate the deleted transaction. (Tip: To easily find deleted transactions, use the browser search Ctrl + F and type "deleted").
5. Under the History column, select View.
6. All the information needed for the transaction can be found under the Event column.

Once you're done, re-enter the invoice using the information from the audit log with its original transaction date.

You can read this article for more details about the Audit Log in QBO: Use the audit log to re-enter deleted transactions.

Also, you may want to check out one of our Help pages as your reference to guide you in managing your company's income and customers in QBO: Sales and customers help for QuickBooks Online. It includes topics about sales and invoice transactions, payments management, and customer statements, to name a few.

Let me know if you have other concerns about managing invoices and income transactions in QBO. I'll gladly help. Take care, and have a great day, @userruben.