Mikescotland
1.I know that ELM327 is a Bluetooth version by default.
2.
A. the dongle is paired either to android system Bluetooth on DUDU - It cannot be connected to any system - it is visible from the Android system but cannot be connected, it is not visible from the DUDU system
B. the dongle is paired to your phone - There's no way it's paired with my phone because when I try, I turn off Bluetooth on the phone, for exactly this reason.
C. the dongle is defective. - It can't be defective because it connects without a problem to my phone and works with its Advancer AD20 app.