Unable to establish 6LoWPAN over BLE connection

I am trying to establish a 6LowPAN over BLE connection between my
Ubuntu Laptop and Raspberry Pi 4B. Laptop is running Ubuntu
5.8.0-48-generic #54~20.04.1-Ubuntu and my RPi is running custom
yocto-based Linux distro with kernel version 5.4.x version.

I am facing an error of 0x12 when trying to establish to Rpi from the
laptop as below:
```
root@root1-Nitro-AN515-55:/home/root1# lsmod | grep 6low
bluetooth_6lowpan 28672 0
6lowpan 40960 8
nhc_fragment,nhc_dest,nhc_ipv6,bluetooth_6lowpan,nhc_hop,nhc_udp,nhc_mobility,nhc_routing
bluetooth 581632 31
btrtl,bluetooth_6lowpan,btintel,btbcm,bnep,btusb
root@root1-Nitro-AN515-55:/home/root1# echo 1 >
/sys/kernel/debug/bluetooth/6lowpan_enable
root@root1-Nitro-AN515-55:/home/root1# dmesg
root@root1-Nitro-AN515-55:/home/root1# echo "connect DC:A6:32:F2:CB:46
1" > /sys/kernel/debug/bluetooth/6lowpan_control runn
root@root1-Nitro-AN515-55:/home/root1# dmesg
[239155.542994] Bluetooth: hci0: request failed to create LE
connection: status 0x12
```

Running btmon in another shell resulted in the following error:
```
< HCI Command: Unknown (0x08|0x0036) plen 25 [hci0] 7.382842
        00 15 00 00 00 00 00 00 00 07 00 01 46 cb f2 32 ............F..2
        a6 dc 00 7f 01 00 01 00 00 .........
> HCI Event: Command Complete (0x0e) plen 5 [hci0] 7.383757
      Unknown (0x08|0x0036) ncmd 1
        Status: Invalid HCI Command Parameters (0x12)
        01 .
* Unknown packet (code 17 len 14)
```

Additional Info: using bluetoothctl between my Laptop and RPi s successful but 6LowPAN is unable to go through.

Any missing from my end?