Will there be any issue if I double side tape the esp8266 on top of the relay like so?
I’ve yet to see one of these relay modules without a back emf diode across the coil so that is unlikely be an issue.
However, arcs from the relay contacts opening might interfere with wifi reception. How much power are you switching?
The relay interrupts the power to aa glade automatic spray running on 2 AA batteries.
It’ll be fine.