[Solved] SF-501PFR Wireless Switch Activation Issue with Remote Control

One of the three switches I recently bought started to behave strangely, i.e. it does not switch on when a signal is given from the remote control, only when I lightly tap it on the housing, does it start to work. Once it is switched on, there is no problem with switching it off, but when I try to switch it on again, it does not work. At the beginning they all worked normally. Please give me some advice on how to rectify the fault. I would like to add that when I want to switch it on (without knocking) the light comes on but the relay does not start, when switching it off the light goes out.

Thank you for your instructions and best regards.

The relay was broken but after a small adjustment it started to work.
thank you and best regards.