1 error prohibited this user from being saved: Confirmation token is invalid

I do register with confirmation email on localhost:3000. in my development.rb i add like this

config.action_mailer.default_url_options = {:host => 'localhost:3000'}
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
    :address => 'smtp.gmail.com',
    :port    => '587',
    :authentication => :plain,
    :user_name  => 'myemail@gmail.com',
    :password       => 'mypassword',
    :domain  => 'localhost:3000',
    :enable_starttls_auto => true
}

when i registers already i open my email and then in inbox show message You can confirm your account email through the link below: Confirm my account i click on this link. it redirect to localhost:3000/users/sign_in and i can login successfully .but when i click on this link (Confirm my accoun) in my inbox again .it show errors like this :

in url : http://localhost:3000/users/confirmation?confirmation_token=dWUeHVP_N7VzsVwvkNW5

meassage errors:

Resend confirmation instructions
1 error prohibited this user from being saved:
Confirmation token is invalid

in my email inbox when i click on link "Confirm my account" again i want it redirect to localhost:3000/users/sign_in. how can i redirect to localhost:3000/users/sign_in when click on link "Confirm my account " again ? please help me!

You can use confirmation link only once after confirmation confirmation_token become nil and causes this error. If you want to redirect some one to sign_in url if confirmation already done. Then you need to override devise confirmation controller.

def show
  self.resource = resource_class.confirm_by_token(params[:confirmation_token])
  if resource.errors.empty?
    set_flash_message(:notice, :confirmed) if is_flashing_format?
    sign_in(resource_name, resource)
    respond_with_navigational(resource){ redirect_to after_confirmation_path_for(resource_name, resource) }
  else
    redirect_to new_user_session_path
    #respond_with_navigational(resource.errors, :status => :unprocessable_entity){ render :new }
  end
end