Puck2.js Master/Slave: probem (red LED) when establishing the connection

I have the pucks named "c123" (master), and "ae23" (slave).
I followed the description at https://www.espruino.com/Puck.js+Controlling+Other+Pucks
1) slave: code copied to puck named "ae23" and save()
2) master: puck name changed to "...filters: [{ name: 'Puck.js c123'..." , code copied and save()

Testing with and without loading "require("ble_simple_uart")" on WEB IDE via "Send to Espruino"

The result is always
a) master: the blue LED is on (OK), then the red LED is on (KO)
b) slave does nothing

What do I do wrong?
Thanks for the answer!