Bluetooth, like your iPhone's other connectivity functions, requires activation in order to function. As a result, be certain you do so ahead of time. Another possibility is that the Bluetooth device you're attempting to connect to is too far away from your iPhone, rendering it inoperable. Unlike Wi-Fi, Bluetooth only operates within 30 feet of each other (may vary depending on the Bluetooth system). Your devices will not be able to communicate through Bluetooth if they are outside of that range. As a result, you should think about changing the distance between your Bluetooth device and your iPhone 6s Plus.