Is this plugin for Deposit reminders?
Events Booking - Payment Reminder
This plugin check and send deposit payment reminder emails to registrants automatically

Is this Plugin for the balance after paying the deposit reminder ?
Events Booking - Offline Payment Handle
This plugin check and send reminder to registrants automatically certain days after registration completed to remind them to complete payment.

Is it possible to use both?
One to remind for the deposit and the other for the full offline payment ?

Sure, nothing to prevent you from using both. It will just work well for both deposit reminder and full offline payment reminder.

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