Question about KingSmith WalkingPad R2

So: I wanted to use the treadmill again (for about the 5th time). And an annoyingly persistent error message "E04" (Low-Voltage Protection) lights up penetratingly. But now nothing works at all. At least the operating instructions list the error code ... but a suggestion for a solution would be really helpful. How can I solve this annoying problem? Many thanks to the community!