Set an Unset Property
This API enables you to set user properties of your users listed in your [User Profiles](../user-profiles-overview) **only if it is currently unset.** If the given payload contains a mix of properties that are currently set and unset, then it will only add values to the properties that are currently unset and ignore the other properties. If the user with distinct ID doesn't exist, it creates a new user with the provided distinct ID and sets values for all the provided properties.<br/><br/>**Note:** If a [property was not created earlier](../adding-new-user-property#how-to-add-a-new-user-property-from-user-profile-page), it will create a new property and the data type of the property will be determined based on the data type of the value. For example, if you `$once` a new property called `premium_user=true`, it will create the `premium_user` property with `Boolean` type and value `true`.<br/><br/>The property values can take the following data types:<ul> <li>**String:** Can be alphanumeric and contain a maximum of 255 characters. Example: `user_type=Premium` or `membership_number=ABC123`.</li> <li>**Number:** Can be an integer or a decimal. Example: `ltv=23000` or `cost=20.34`.</li> <li>**Boolean:** Can only contain `true` or `false` values.</li> <li>**Date:** Must be in ISO 8601 format. Example: `membership_date=2020-10-01T18:30:00.000Z` or `membership_date=2020-10-01T18:30:00Z` or `membership_date=2020-10-01T18:30:00.000+05:30` or `membership_date=2020-10-01T18:30:00+02:00` or `membership_date=2020-10-01`.</li> <li>**List:** Can contain an array of strings, numbers, and dates. Example: `products_ordered=['iPhone 16 Pro', 'iPad 32 GB']` or `purchase_amount=[23000, 20.34]` or `purchase_date=['2020-10-01T18:30:00Z', '2021-11-01T13:35:00+02:00', '2023-12-05']`</li> </ul>If you try to set a value with a data type that does not match the predefined property type, the API will accept the request but ignore the invalid value. For example, if a predefined property `cost` expects a numeric value and you try to set it to `ABC`, the API will not store the value.<br/><br/>These user properties can be used to filter your users for creating [user cohorts](../creating-cohorts) and [campaigns](../campaign_creation#creating-a-campaign-using-cohort).