The credit balance warning in the status messages and in the view "Tasks" begin when the total credit is less than 2€ x the number of active devices.
Example: You have 8 active devices. 2€ x 8 active devices = 16€. If your credit falls below 16€, you will receive a credit warning that your credit is low.
In this way you always have enough time to recharge, even if you are e.g. on vacation.
From 0.70€ x the number of devices, you will also receive a warning on the critical channel that you selected in your settings (before only in the status messages and in “Tasks”).