Maybe u'r phone is not compatible.
U Can check this on the answer from Ryze on a previous post on Dji official forum.
Hey， your device Huawei P9 is not in the compatible list yet. Please kindly check the compatible devices below. Thanks.
Requires iOS 9.0 or later. Compatible with iPhone 5s, iPhone SE, iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPad mini 4 and iPad mini 4 Wi-Fi + Cellular.
Android version 4.4.0 or later. Compatible with Samsung S7，Samsung S6 edge，Samsung S5，Samsung Galaxy note 4，Samsung Galaxy note 3，Huawei Honor 8，Huawei Honor 9，Huawei P8 Max，Huawei P10，Huawei Honor V8，Huawei P9，Huawei nova2，Xiaomi 6，Xiaomi Note3，Redmi 4A，OnePlus5，vivoX6，Google Pixel1 XL，Google Pixel2."
Hope this Can help U
I've only used the 'internet' to download the APP...
The Tello has its own wifi sys, and so does your smart phone,
weather an IOS or Android...
The smart phone is connected to the Aircraft thru its own connection,
with no need for the internet. If you have a 'Gamsir T1d' controller, then
that is connected thru Bluetooth.
Ergo, no need for the internet. I get that alert/error all the time when
connecting. but it goes away when I'm finally up and running.