Not getting user ID in access token

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I also tried to add custom claim in login/post login action like

exports.onExecutePostLogin = async (event, api) => {

console.log("ACTION STARTED");

  if (event.authorization) {

console.log("USER_ID",event.user.user_id);
    // Set claims 
  api.accessToken.setCustomClaim(`user_id`,event.user.user_id);
  }
  console.log("ACTION COMPLETED");
};

still this user_id is not showing up in access token payload.