Hello,
If you can watch the Tivimate app on your wifi but can't watch over your cell plan it is because on wifi you have a public ip address. When you are using your cell plan to stream you have something called CG-NAT, which means you don't have an actual public IP address on your phone. To stream using your cell phone plan you need to use a VPN because a VPN will assign a public ip address to your phone.
