Invoices sent to a customer says it has been paid when it hasn't.(so its behaving like a receipt)

Hi there, @guardianofall.

It's nice to have in the Community. I'd be happy to help get this invoice concern taken care of today.

When you emailed an invoice to your customer, and it's showing a paid status, it's possible that the Automatically apply credits in your settings is turned on. If the customer has an existing credit or overpayment, QuickBooks Online will automatically apply that credit to the newly-created invoice.  

To fix this, you'll need to turn off the Automatically apply credits option in QuickBooks Online, so your customer's credit will not be applied to the current invoices and will mark it as paid.

To turn it off:

1. Select the Gear icon.
2. Click Account and Settings. 
3. Tap on Advanced on the left of the screen.
4. Click the Pencil icon in Automation.
5. make sure to disable the Automatically apply credits option. 
6. Click Save and select Done.

Once done, we can now delete the payment that was associated with the invoice. This way, the invoice will be marked as unpaid, and you can send it again to your customer.

Here's how:

1. Open your customers invoice and double click it.
2. On the Payment Status section, click the 1 payment link and tap on the Date hyperlink. 
3. Press on More.
4. Choose on Delete. 
5. Click Yes to confirm.

Lastly, I'm adding here a link that you can read through about sending and paying invoices online in QBO: Take and process payments in QuickBooks Online.

Should you need additional assistance about this or with QuickBooks, please let me know. I'll be around for you. Take care.