@Kirkybaby When you are adding Satellite Deco to your Deco mesh, it must be able to communicate with Main Deco. Bring new M5 to the room where Main Deco is, power M5 on, do not connect it by Ethernet...

@Shigeru_Lloyd In theory, if Satellite Deco can't connect to Main Deco, it'll try to connect to another Satellite Deco. I wonder if something is up with new M4 you bought. Try this: 1. Place 'new' M4...

@Napalmo0 This switch should be compatible. Reminder: your setup will only work with Deco in Access Point mode, I would suggest connecting Satellite Deco to the switch only after you configured Deco...

@Vassilis Set password for Guest Network exactly the same as it is for Main Network. If Redmi won't connect to Guest Network after that, take careful look at password and special symbols in it. Start...

@36ty That means Satellite Deco can use both bands for devices that try to connect to it. The next step would be to promote Satellite to Main Deco, swap Deco units and see if problem moves with Deco...

@HeinvL I can offer you a workaround for about $50. What you will need: 1. Two very short Ethernet cables, Cat 5E or Cat 6, that work with M5. Test them by bringing third M5 to where second M5 is and...