Hello everyone,
I finally took the time to get back to the subject and to do what @_Will_71 had suggested, to replace the impulse relay with the sonoff. It’s done and it works very well. I kept all the wires that were connected to the impulse relay (except the neutral) and put them directly on the sonoff (using the Lout, Lin, and S2 connections).
And I, who didn’t want to remove the impulse relay to have better reliability, realize that