Buy N items and get M of the same item for free

Specify in the price list how many items need to be purchased and how many the customer will receive as a gift.

Structure

<promos>
   <promo id="promo ID" type="n plus m">
      <start-date>promo start date</start-date>
      <end-date>promo end date</end-date>
      <description>summary</description>
      <url>promo on the store's site</url>
      <purchase>
        <required-quantity>number of full-priced items</required-quantity>
        <free-quantity>number of bonus items</free-quantity>
        <product offer-id="offer ID participating in promo"/>
        ...
        <product category-id="category ID participating in promo"/>
        ...
      </purchase>
   </promo>
</promos>

Attributes and elements


Element/attribute	Description	Required
Attribute `id`	ID of the promotion. Must be unique for the entire price list. It may contain only numbers and Latin letters. The maximum length of `id` is 20 characters. Attention. Each offer can only participate in one promotion.	Required
Attribute `type`	Type of promo — `n plus m`.	Required
`start-date`	Date and time when the promo starts. Allowed formats: `YYYY-MM-DD hh:mm:ss` or `YYYY-MM-DD`. The date and time are the same for all time zones. Example The store sells products in Moscow and delivers to Yekaterinburg; date and time of the promo: from 10 AM on March 8 to 10 AM on March 9. For users in Moscow, the promo will run from 10 AM on March 8 to 10 AM on March 9 (Moscow time). For users from Yekaterinburg, it will be from 10 AM on March 8 to 10 AM on March 9 in the Ural time zone.	Optional
`end-date`	Date and time the promotion ends. Allowed formats: `YYYY-MM-DD hh:mm:ss` or `YYYY-MM-DD`. The date and time are the same for all time zones (see the example above).	Optional
`description`	Brief description of the promo in Russian. Maximum of 500 characters. You can use XHTML markup, but only as a `CDATA` block of character data.	Optional
`url`	Link to the promotion description on the store's website.	Optional
`purchase`	Information about items participating in the promotion.	Required
`required-quantity`	The number of items that must be purchased in order to receive a gift. This element is in `purchase`.	Required
`free-quantity`	The number of items the customer will receive as a gift. This element is in `purchase`.	Required
`product`	Items and/or categories that the promotion applies to. Attributes: `offer-id` — Offer ID. `category-id` — Category ID. Each `product` element corresponds to a single item or category. A `purchase` element may contain multiple `product` elements.	Required


Element/attribute	Description	Required
Attribute `id`	ID of the promotion. Must be unique for the entire price list. It may contain only numbers and Latin letters. The maximum length of `id` is 20 characters. Attention. Each offer can only participate in one promotion.	Required
Attribute `type`	Type of promo — `n plus m`.	Required
`start-date`	Date and time when the promo starts. Allowed formats: `YYYY-MM-DD hh:mm:ss` or `YYYY-MM-DD`. The date and time are the same for all time zones. Example The store sells products in Moscow and delivers to Yekaterinburg; date and time of the promo: from 10 AM on March 8 to 10 AM on March 9. For users in Moscow, the promo will run from 10 AM on March 8 to 10 AM on March 9 (Moscow time). For users from Yekaterinburg, it will be from 10 AM on March 8 to 10 AM on March 9 in the Ural time zone.	Optional
`end-date`	Date and time the promotion ends. Allowed formats: `YYYY-MM-DD hh:mm:ss` or `YYYY-MM-DD`. The date and time are the same for all time zones (see the example above).	Optional
`description`	Brief description of the promo in Russian. Maximum of 500 characters. You can use XHTML markup, but only as a `CDATA` block of character data.	Optional
`url`	Link to the promotion description on the store's website.	Optional
`purchase`	Information about items participating in the promotion.	Required
`required-quantity`	The number of items that must be purchased in order to receive a gift. This element is in `purchase`.	Required
`free-quantity`	The number of items the customer will receive as a gift. This element is in `purchase`.	Required
`product`	Items and/or categories that the promotion applies to. Attributes: `offer-id` — Offer ID. `category-id` — Category ID. Each `product` element corresponds to a single item or category. A `purchase` element may contain multiple `product` elements.	Required

Example

Buy two bags of dog food and get the third free:

<promo id="Promo2Plus1" type="n plus m">
  <start-date>2018-02-01 12:00:00</start-date>
  <end-date>2018-03-01 12:00:00</end-date>
  <description>Купи 2 упаковки корма и получи третью в подарок!</description>
  <url>http://best.seller.ru/promos/2plus1</url>
  <purchase>
    <required-quantity>2</required-quantity>
    <free-quantity>1</free-quantity>
    <product offer-id="55"/>
    <product offer-id="66"/>
    <product category-id="1"/>
    <product category-id="2"/>
  </purchase>
</promo>