The E1 fault has to do with the water sensor. It now measures an empty tank when that is not the case. Fortunately, you can reset this sensor briefly so that this message is no longer displayed incorrectly.
Follow the steps below to solve your problem.

1 - Switch off Beam mini (2) and disconnect from the mains;
2 - Beam mini (2) consists of a bottom (the water tank) and a top (the water tank);
3 - Remove the top of Beam mini (2) and set it aside temporarily, preferably in a sink;
4 - Remove the water from the bottom of Beam mini (2);
5 - Put the plug in the socket;
6 - Press the minus sign on the remote control until you hear a beep;
7 - Put the top, including the water, back on Beam mini (2);
8 - Wait a moment until the water has drained out of the water tank;
9 - Switch Beam mini (2) on again, the E1 message should no longer be visible.