@CitySlickerRancher has useful information. However, it is remarkable that this many years after this issue was raised so many times there is still no way to alert multiple emails that a payment was made, or even to choose to alert an email that is not your main customer service email.

Please do not respond saying that you see how this would be useful or to visit the Merchant Center and change my settings for alerts or to check the spam folder.

Potential solution: If you're willing to pay for, or already use Zapier, it appears this is an easy 2 step zap to create based on the Quickbooks "New Payment" trigger.