Rails AASM does not rollback when validation returns false

Question

I have a model Booking that changes the status using AASM

models/booking.rb

before_validation :item_availability, if: -> { pending? || approved? }

enum status: [:pending, :approved, :rejected, :on_loan, :returned]

aasm column: :status, enum: true, whiny_transitions: true do
  state :pending, initial: true 
  state :approved

  event :approve do
    transitions from: :pending, to: :approved
  end
end

private
 def item_availability
    if quantity.to_f > item.quantity.to_f
      errors.add(:base, "Not enough quantity for #{item.name} only #{item.quantity} left")
      false
    end
  end

and I have a service that triggers the approve! event

  def run
    booking.transaction do
      booking.approve! 
      booking.item.decrement!(:quantity, booking.quantity)
      BookingsMailer.send_approval(booking).deliver_now
    end
  rescue ActiveRecord::RecordInvalid => e
    errors.add(:base, e.message)
    false
  end

The problem here is the validation is being hit because the quantity is greater than the booking's quantity but the transaction in my service does not rollback.

According to documentation

Saving includes running all validations on the Job class. If whiny_persistence flag is set to true, exception is raised in case of failure.

I already set whiny_transitions to true but