Payment not made but not showing up in incomplete payments

Incomplete payments have been showing up.  But I got notification of one submission but payment was not made and it does not show up in incomplete payments.  Why would some show in incomplete payments and some do not?

Hello,

I can see that payment field is not required on your form, so if respondent will not select any product on that field, the form can still be submitted. This type of submission will not go into Incomplete Payments, because the form does not require a payment.

If needed, please follow the screenshot to set the payment field required:

We will gladly assist if you need any further help.