When connected to a Bluetooth device in android os, it is indicated in blue to check the connection status. enter image description here
When I paired the Arduino device and launched the app, I connected the GATT and got the signal.
But I don't know why the color of the device doesn't change to blue, and there's a toast saying, "Install the apps you need to use this device." enter image description here
Please let me know if there's a solution.