Trying to send an invoice, when saved it says paid straight away & back dates the payment. even though i didnt get to send invoice to my customer

Hi there, @j-and-s-turflayi.

Turning on the Automatically apply for credits in the Account and Settings will reduce the customer's current balance. The system will tag the invoice as paid when there's a payment recorded or linked to it. You can remove the watermark PAID by reverting the status of the invoices to unpaid. 

1. Open the invoice and click the payment link below the Payment Status Paid in the upper right corner.
2. Then, tap on the date link.
3. On the Receive Payment page, click the Clear Payment button.
4. Hit Save and close.

Once done, the invoice will be open again.

Also, to stop the system from automatically apply the credits or unapplied payments to the open invoice. Follow the steps below on how to turn it off:

1. Click the Gear icon.
2. Select Account and Settings.
3. Go to the Advanced tab.
4. Click the Pencil icon in the Automation row.
5. Uncheck the Automatically apply credits box.
6. Click Save, then Done.

Although, if you've turned off the feature already, you can still see the credit or unapplied payment when you record the payment manually. If you're not going to apply it to the invoice, ensure not to select the credit. For reference, see this article: Create and apply credit memos or delayed credits in QuickBooks Online.

Just in case, I'll be adding these articles for future reference on how to manage your invoice transaction:

• Record an invoice payment.
• Send invoice reminders automatically or manually in QuickBooks Online

Feel free to leave a comment if you have any additional questions or other concerns. Thanks. I'm always here to help. Take care.