PZEM04 CF pin

Hi bougth a (old?) PZEM04T V1.0 from Aliexpress. I found connector that face with (in my case) ESP8266 don’t have 4 but 5 pins. There is a pin called CF. Anyone knows what this pin is for? Thanks for your help.

as I know , this is kwh output
1 kwh=1 pulse