Also, it’s not clear how large the tracks are that handle the mains power, or how much physical separation there is between them and the low voltage connections to the relay. If you take a look at some similar boards such as the Sonoffyou’ll see that additional so,Der is flowed over the mains tracks (which are already quite wide) to beef them up, and parts of the circuit board are routed out to provide an air gap between the HT and LT sides. hT tracking across the surface of the circuit board can be an issue in high humidity or dusty environments.
Pete.