I am trying to integrate with Slack where i am using https://slack.com/api/users.list which is pulling all the user details but i unable to see the Birthday date. Can anyone please help me how to get the user birthday date
The birthday of a user is not a standard field in Slack. That is why you do not get it from users.list.
If you want to work with birthday's you have two options:
You can add it as custom field to users with users.profile.set (only on paid teams).
Or you can run your own birthday day storage (e.g. the Slack app having its own database) for your bot (which is what most birthday bots do).