diff --git a/README.md b/README.md
index b9c3f93..0b17b50 100644
--- a/README.md
+++ b/README.md
@@ -96,6 +96,7 @@ The action accepts the following parameters:
 | <nobr>`user_telephone`</nobr>          | String  | The telephone number of the contact                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                 |
 | <nobr>`user_company`</nobr>            | String  | The company of the contact                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                 |
 | <nobr>`user_extrafield`</nobr>         | String  | Additional information of the contact                                               |                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                 |
+| <nobr>`campaign_id`</nobr>             | Integer | The CiviCRM ID of a campaign to assign the contribution                             | A valid CiviCRM Campaign ID. This overrides the campaign ID configured within the profile.                                                                                                                                                                                                                                                                                                                                    |                                                                 |
 
 You may also refer to
 [the code](https://github.com/systopia/de.systopia.twingle/blob/master/api/v3/TwingleDonation/Submit.php)