Let's make sure to fix the issue and guide you on what to do, Deborah.
It's possible that the automatically apply credits option is turned on, that's why invoices get paid automatically as soon as you send them to your customers.
You can undo the payment on the invoice by clicking the 1 payment link:
Then, click Clear Payment.
After that, click Save and close. You'll receive a prompt that tells you the transaction is linked to others, click Yes. Then, you can send the invoice to your customers.
Once you're done correcting your transactions, ensure to turn off the option. Here's how:
Go to the Gear icon, then Account and settings.
Click Advanced, under the Automation section, click the pencil icon.
Toggle to turn off the Automatically apply credits option.