If you do not want such reminders to be sent, go to your account, select Projects and Activities > My Projects and click Project settings > Paysera Checkout settings next to the project.
In "Notifications for payers", check the box: Do not send reminders to clients who had started a payment process, but never completed it. A reminder is usually sent after 3 hours and only for those online payment methods which take up to 15 minutes to complete.