I received payment before I actually received payment. Now the client can't pay the invoice as it says paid. How can I open that invoice so she can pay.

Welcome and thanks for visiting the Community, @userlblack.

If you manually recorded the payment in QuickBooks Online (QBO), you can delete it so your client can pay it through QuickBooks Payments.

Here's how to do it:

1. In QBO, go to the Sales menu at the left pane to get to the Customers page.
2. Click the customer's name to open the Transaction List.
3. Locate the payment and select it to open.
4. Tick the More option at the button and choose Delete. 
5. Hit Yes to confirm. The customer will have an unapplied payment which you can either delete or apply to future invoice(s).

Once done, your client can now pay the invoice by having them click the Pay Now button. I'm also adding this article that tackles how to let customers pay their invoices online for future reference: Take and process payments in QuickBooks Online.

Please leave a comment below if you have any additional questions or concerns. I'll be more than happy to help. Have a great day!

This did not resolve my problem. I followed your steps and the invoice disappeared. 

Now I am totally confused. Can I talk with a live person?

To recap.

I accidently received payment on an invoice when no payment was made yet. How do I reopen the invoice so that my client can pay the invoice?

Thank you.

Lynn

Thanks for coming back for more support, @userlblack. I appreciate you for trying the steps provided by my peer. 

It could be that the invoice itself is deleted instead of the payment attached to it. We can check your audit log confirm. I'll show you how: 

1. Click the Gear icon, then select Audit Log. 
2. Filter the transactions from the Filter drop-down arrow, then click Apply.
3. Locate the invoice and see if it is deleted. 

Once confirmed, you'll need to re-enter the transaction and resend it to your client. You can get the full details of the deleted invoice by clicking View under the History column.  

For future reference, you may follow the steps shared by my colleague in this post to remove a payment from an invoice. 

Should you still need to speak to a live person online, you can choose either chat or callback option to connect with our Customer Care team.  

I'm always around here to help you some more if you need further assistance.