I sent out an invoice and it’s saying that the invoice is paid and I haven’t received payment immediately when I sent out the invoice.

I've got you covered, msmith.

Situations like this occur when the Automatically apply credits feature is enabled, causing a customer's existing credits to be applied to any open invoices, resulting them being marked as paid immediately.

To verify this, let's check if this has been turned on.

1. Go to the Gear icon and select Account and settings.
2. Head to the Advanced tab.
3. Select the Automation section, then check if the Automatically apply credits option is turned on.

If you confirm that the option is enabled, it explains why the invoice has been automatically marked as paid. 

For reference, check out this article: Create and apply credit memos or delayed credits in QuickBooks Online.

Also, you can check from your Sales menu to see if credits were applied to the invoice. To do so, here's how:

1. Go to Sales.
2. Select All Sales.
3. Locate the invoice.
4. From the Status column, check if credits have been applied.

Additionally, if you want to manage your sales transaction records, you can check out this article for guidance: Run reports in QuickBooks Online.

Feel free to reply to this post if you have other questions about invoices and payment processes in QBO. I'll make sure to help you out anytime.