There is a known Android Bluetooth connectivity issue - Monimoto does not work with Android 6.0 (Marshmallow). This version of Android is causing connectivity issues between Monimoto and devices running this OS. There is nothing we can do about this as many other manufacturers encounter this issue too. The only solution to this issue is to upgrade your phone to Android 6.0.1 or higher.
Android 6.0.1 has addressed Bluetooth connectivity problems and Monimoto works well with it.
Here are some of the phone models that have been tested and proved to be working with Monimoto (with Android versions other than 6.0):
Huawei P9 Lite
HTC One M7
HTC One M8
LG Nexus 5X
OnePlus 2 (Most OnePlus need restart phone before pairing)
Samsung S5 (hard to connect to S5 NEO)
Samsung Note 3
Samsung Galaxy Note 8
Xiaomi Redmi Note 4
Xiaomi Mi A1 (some need restart phone before pairing)
Xiaomi Redmi Note 5 has pairing issues
Huawei P8 lite
BLU Vivo 6