Review on Keyestudio 5V DCAC 4-Channel Relay Hat Shield Module Expansion Board for Raspberry Pi 4, A+, B+, Pi 2 Model B, Pi 3 Model B by Jennifer Lawson

As mentioned before, the following relay GPIO card worked great for me: gpio 4 is relay 1 gpio 22 is relay 2 gpio 6 is relay 3 gpio 26 is relay 4 others too have mentioned that the relay controller mounting hardware doesn't quite fit the board (leaves small gaps, see attached pictures), but it still works. Another thing I want to mention is that you need to know the height of the heatsink you have on the PI processor. . If the heatsink is too high, it will prevent the relay controller from installing properly and may cause equipment damage if the heatsink and relay controller come into contact. I learned it the hard way.