I have -open showing 9n a customer account all invoices are paid what does this mean

I'm glad to see you here in the Community. callumsmith336.

Let's verify your customer's balance by reviewing the paid invoices and payments in QuickBooks Online.

It's possible that you linked the payment deposit directly to your invoices without recording any payment. That's why, there's an open balance and your invoices are showing as paid.

To resolve this, we can change the account for the deposit to make sure it syncs with the invoice.

Here's how: 

1. Go to Accounting.
2. Choose Chart of Accounts.
3. Select the bank account in which you deposited the customer’s payment. Then click Account history.
4. Tap on the deposit, then click Edit.
5. In the Add funds to this deposit section, find the deposit.
6. Select the Received From ▼ dropdown, and select the customer the deposit was from.
7. Tap the Account ▼ dropdown. Then select Accounts Receivable.
8. Click on Save and Close.

To learn more about receiving and categorising invoice payments in QuickBooks Online, check out this article: Record invoice in QuickBooks Online.

I'm adding this link to guide you once you're ready to reconcile an account in QuickBooks Online.

I'd like to make sure everything clear. Don't hesitate to leave a comment below for follow-up question. Have a great day!