I am using a password change ticket method to invite I want to update the user_meta by asking using permission what can I do for that?
Could you please explain a little bit more about what you would like to include in the user metadata? Also, at what point would you need to alter the user metadata (when the user is created or when they log in, etc.)
I m using a user invitation-based system where an admin can invite the user and for that, I m using the password change token method to do so. The problem is that if the user is already existing in the database admin is unable to send an invite to him what I can do to fix it?
The password-change email can be sent to users who already exist. Are the admin adding the users manually or are you generating a password change ticket for existing users?:
You may find this topic answer helpful for setting up a hook that sends a password change email when a new user is created:
Here is additional documentation on invitation-based flows: Send Email Invitations for Application Signup