Replacing Airtel Zxyel AOT-5221ZY with Digisol ONT DG-GR6011

Hi Guys
I am trying to connect Digisol ONT on one of my Airtel broadband connection while PON is operational I am unable to connect to PPPoE.
I have already changed GPON_SN to zyxel serial number and PON_VENDOR_ID ZYXE on Digisol.

Please suggest what could be wrong due to which it is rejecting PPPoE requests.

Vendor ID is ZYOT