If there is no power going to the keypad, this could be either a power issue or a keypad issue. To check, try connecting to the Bluetooth within the Sauna. If you can see it available on your device, it means there is power going to the sauna, and therefore the issue must be with the keypad.
Regardless of cause, a hard-reset is always the first thing to try with any power or keypad issue. Unplug the sauna from the mains power, let residual power drain out for 60 seconds, and reconnect.
If the keypad is identified as the issue, see our article 'How to check keypad cable connections'.