MyQ (Chamberlain) garage door and Gateway 5G router not compatible

@fitisit2012  If I understand correctly, your home security system was working with the first gateway.  So the technician should not have said "nobody has T-Mobile internet" or that Vivint doesn't work with T-Mobile internet.  Do you remember if the first gateway had more than one Wi-Fi network? They come with one, but more can be added.  Many people have added a second network to handle garage door openers, printers, older computers, etc.  Your first gateway might have had that, and now your Vivint system can't find it because it doesn't exist (yet) on the replacement gateway.  Please read the instructions for creating a second network in my post which is the last one on Page 1.  Do you remember if you or someone else did that before?  Do you know the SSID (network name) and password that the system was using?  If you can remember, make a new network on the new gateway with the same SSID and password as before.  If you can't remember, you should go through these steps -- but you will also need to connect the security system to the new network.  You may have to have the technician return.  You might need to show him the T-Mobile Internet (or T Life) app on your phone.  Avoid changing any settings for the first network which I am assuming is working for other devices in your home.