ActiveRecord::RecordNotFound: Couldn't find ModelName with ID= when using accepts_nested_attributes_for

Question

For example, I have three model classes:

class Promotion < ApplicationRecord
  has_many :promotion_sets, dependent: :destroy
  accepts_nested_attributes_for :promotion_sets
end

class PromotionSet < ApplicationRecord
  belongs_to :promotion
  has_many :promotion_set_details, dependent: :destroy
  accepts_nested_attributes_for :promotion_set_details
end

class PromotionSetDetail < ApplicationRecord
  belongs_to :promotion_set
end

I want to insert. For example here is my code:

  Promotion.create(id: 999)
  promotion.promotion_sets
   .create(prepare_promotion_set_attrs(attributes['promotion_sets']))

Then those are methods for preparing children attributes:

def prepare_promotion_set_attrs(set_attrs)
  promotion_sets_attributes = []
  set_attrs&.each do |attr|
    promotion_sets_attributes.push(
      id:  123456,
      promotion_set_details_attributes: prepare_promotion_set_details_attrs(attr['set_details'])
    )
  end

  promotion_sets_attributes
end

def prepare_promotion_set_details_attrs(set_detail_attrs)
  promotion_set_details_attributes = []
  set_detail_attrs&.each do |attr|
    promotion_set_details_attributes.push(
      # sample fields here
    )
  end

This insert is successfully execute. But when I move insert code from inserting outside to accepts_nested_attributes_for for only class Promotion:

Promotion.create(
        id: 999,
        promotion_sets_attributes: prepare_promotion_set_attrs(some_data),
      )
# not use this 
# promotion.promotion_sets
#   .create(prepare_promotion_set_attrs(attributes['promotion_sets']))

I meet exception:

ActiveRecord::RecordNotFound: Couldn't find PromotionSet with ID=123456 for Promotion with ID=999

I cannot explain why. And I don't know why this is just only happen for class Promotion but class PromotionSet can insert using accepts_nested_attributes_for without any error.