Check to see if you are trying to connect it to 5G. I decided to try the 2.4G and that was the fix I needed.(my router supports both)
My MFC-2701DW will not connect to 5G. I wish that information was given to me clearly from Brother. So, how I proceeded.
I did reset the network on the printer (option in the network section of the the printer)
Rebooted the printer.
Went into setup Network - WLAN(Wifi)
Found the SSID and entered it then it asks for the key, typed it it..it said connected right away.
If you need or want more info, ask here. I will try to pay attention to this thread.
Hope this helps someone.