Like I said above, try deleting all the stored credentials for any other wifi networks your 740 has ever connected to. Then, try to connect to the network and input the password as required.
But also as I said above, it would be better to go through that process in the plane, and connect the 740 to your ADSB network and then never connect it to anything else. Build your flight plan on your phone in your house, in your hotel, in the FBO, wherever you want, but leave it there until you get to the plane. Once you're in the cockpit and the 740 is powered up and connected to the wifi in the plane, then make sure your phone is also on that network, push the flight plan over to the 740, and go fly.