Nighthawk X6S AC3000 Unable to connect to an outdoor device

[GMORE]

I am unable to connect to a 2.4 GHz devise-outdoor Recteq grill.  I am using their app for wifi connection and instructions.   The indoor router is aprox 40ft max from the grill and the signal must travel thru two interior and one exterior walls. Instructions have been followed and the grill light blinks, but the grill and iphone will not connect.  Please advise, I need help. Thx

[plemans]

What modem/gateway do you have the router connected to? 

What are the exterior walls of your home made of? Things like metal (steel siding), brick,adobe, etc are all great at blocking wifi. 

when you're setting it up, do you have your iphone on the 2.4ghz signal? That's another key.