Update a attributes list

This endpoint allows you to update an existing list attribute by replacing its values with a new one-column list. The request body must be plain text, with one value per line.

Constraints

• Max request body size: 15MB
• Max attribute name length: 25 characters
• Max attribute description length: 50 characters

📘

Note:

• The request body must contain one value per line, with a maximum body size of 15 MB.
• Updates via this API are processed immediately on the backend. However, list-based matching in campaigns is refreshed once daily at the time the list was originally created.
  For example: If a list was created at 3 PM, any new values added later will only be matched starting 3 PM the next day.

⚠️ Do not include Personally Identifiable Information (PII) such as email addresses, phone numbers, or full names in the list.

Instead, use a hashed value or an anonymized identifier that:

• Can be accessed from the browser (e.g., via cookies or local storage) for client-side targeting
• Is available in your server logic (e.g., user ID or hashed email) for server-side targeting

Using a consistent, non-PII identifier ensures safe and reliable matching across client and backend integrations.

user_1
user_2
user_3