Welcome to the Intuit Community, rtong.
Thanks for reaching out to us about getting rid of the email reminders.
Right now, you're unable to disable emails for the customer payments in QuickBooks Online. With regards to this option, I believe the more added flexibility the product has, the more it will appeal to the wider audience.
I've added this request to our own internal product enhancement list, which we send directly to our product development team. Our updates are based on the suggestions we and the engineers receive from our customers.
I encourage you to send feedback directly to our development by clicking the Gear icon and selecting the Feedback option. This will help us identify what product feature/option your business works best.
I'm here anytime you need assistance concerning your QuickBooks Online. Wishing you all the best.