So I tried to set up my slave deco ‏and even I had a stable ‏blue light  I couldn't have a good wifi signal. 

I tried to remove the slave Deco and connect it again but it still didn't work. I tried to connect it via Ether net and also failed, so I checked if I there are updates to the firmware. 

I saw that the main Deco and the slave Deco have different versions so I wanted to update the version of the slave Deco. 

Then I found out ‏i can't update the version of ‏‏the slave Deco. 

I had to set up a new network and put the slave Deco as the main deco and then I could uodate it. 

 ‏i think TP Link ‏‏ should add this feature to the app. 

Tnx.