LG HBS-730 can't be paired with Lenovo P70

[AC Question]

I just bought an LG HBS-730 & tried all night to pair it with my phone Lenovo P-70 (Android 5.1) but kept failing due to incorrect passkey/PIN but of there's no window prompting for passkey/PIN.

However, the LG HBS-730 can be connected to LG P-990 (Android 4.4.4), Asus Zenfone 2 (Android 5.0) & Sony XPeria Z5 (Android 5.1.1). I've installed lots of bluetooth related apps but nothing works.

Please help me to troubleshoot this.