problem_illustration.rb

# controller
def accept_invitation
  if invitation.accepted?
    render json: { errors: ['Invitation already accepted'] }, status: 422
  else
    user = User.build_from_invitation(invitation)
    user.save!
    invitation.accept
    invitation.save!
    UserMailer.notify_affiliate_payment(invitation).deliver_later
    render json: { user: user }
rescue ActiveRecord::ActiveRecordError => e
  render json: { errors: [e.message] }, status: 422
end
  
# User model 
class User < ActiveRecord::Base
  has_many :invitations
  after_create :send_welcome_email
  def send_welcome_email
    if Invitation.where(email: email).exists?
      UserMailer.affiliate_welcome(self).deliver_later
    end 
  end
  def self.build_from_invitation(invitation)
    # logic to build user goes here
  end
end
  
# Invitation Model
class Invitation < ActiveRecord::Base
  before_save :pay_inviter, if: ->{ accepted_changed? && accepted? }
  belongs_to :inviter, class_name: 'User'
  def accept
    self.accepted = true
  end
  def pay_inviter   
    # credit logic goes here
  end
end