Facing issue while authentication with openAm 12

[gitHub1501]

I am using this custom grant handler for open AM 12 .
Open AM 12 does not have the sessionInfo endpoint which has been used in the code here.

Hence I tried to use session_isActive APi of openAm 12.

I am able to get access token using curl command for the custom grant handler "openamcookie", However when invoke the WSO2 gateway APi using this access token as Bearer I get error as unauthorized / forbidden.