Subscribe to a Ros topic with an Android App, developed on Unity

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Hi, I'm currently developing an Android Application to remotely control a robot using ROS. I'm developing this Application with Unity and I'm using the ros-sharp asset to communicate between the robot, via ROS, and my application. Right now i try to subscribe to the camera of the robot and actually it works with the Unity simulation, but if I build my Android Application and launch it on my phone, my phone can't subscribe to the topic of the camera like the simulation do, but the robot tell me that the websocket between the phone and the robot is good. So, why my phone can't subscribe to the topic ?

I have already check on Internet to find an issue but I find no one that use Unity to develop an Android App to communicate with ROS.

Thank you in advance for your answers