> ## Documentation Index
> Fetch the complete documentation index at: https://docs.slm.m1amdocs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Working with Campaigns

Subscribe Campaigns allow you to offer discounts on existing Products, or time grants to existing AutoBills. Discounts may be currency or percentage based, and may be single purchase, or period based offers. Time grants serve to grant customers free time extensions to their existing AutoBills.

Use the Subscribe Portal to define Campaign parameters, then generate and retrieve Campaign Codes. Use the Subscribe API to apply a (Coupon or Promotion) Campaign to an AutoBill.

**Note:** Use of the forward slash character (/) in merchant identifiers is not allowed. See [Merchant Identifiers](Merchant_Identifiers#) for more information.

Subscribe offers several ways in which a Campaign discount may be applied to an AutoBill.

* Use `AutoBill.update` to create an `AutoBill` and apply a Campaign discount Code simultaneously.

* Use `AutoBill.addCampaign` to apply a Campaign Code to an existing `AutoBill`.

* Use `AutoBill.modify` to add a new Product and/or Billing Plan, and its corresponding Campaign discount, to an existing `AutoBill`.

* **[Creating an AutoBill with a Campaign discount](../topics/Creating_an_AutoBill_wit_2)**

* **[Adding a Campaign Code to an AutoBill](../topics/Adding_a_Campaign_Code)**


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