Many thanks you for your answer! I was able to point the receiver to my local mosquitto broker using the mentioned web page.
The only problem is that I do not see any connection attempt from the receiver side to my MQTT server in mosquitto server log and I am not receiving any events. Is there an MQTT connection status page or something similar to debug this?
I can see steady red LED on the right of the USB connector and steady red, orange and green LED on the left. What is meaning of the LEDs?
My problem is probably resolved by using another iBeacon. Yesterday I used LightBlue Bean in the iBeacon mode and it was not detected by iBeacon receiver.
Today I used Zebra MPact iBeacon and everything works as expected.