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

# Why Do the Delivery Error Logs of Gupshup Display UNKNOWN_SUBSCRIBER?

> Fix the UNKNOWN_SUBSCRIBER error in Gupshup WhatsApp delivery logs. Common causes include unregistered numbers and outdated WhatsApp versions.

## Problem

The UNKNOWN\_SUBSCRIBER error is a major factor that causes issues in WhatsApp campaigns.

## Cause

* The issue can be caused by various reasons, including:
  * The recipient's phone number is not registered on WhatsApp.
  * The recipient has not accepted the latest Terms of Service and Privacy Policy.
  * The recipient is using an outdated version of WhatsApp and did not update to the following versions or higher:
    * Android: 2.21.15.15
    * SMBA: 2.21.15.15
    * iOS: 2.21.170.4
    * SMBI: 2.21.170.4
    * KaiOS: 2.21.30.10
    * Web: 2.21.32.6
* Delivery failure may also be due to Frequency Capping (FC), displayed as UNKNOWN\_SUBSCRIBER by Meta.

<Accordion title="How often does Meta engage in capping?">
  - FC by Meta limits marketing messages sent to users in India.
  - It aims to reduce message overload and improve the ROI.
  - FC for marketing messages applies only to users in India (+91).
  - This limit only affects new marketing conversations, not ongoing ones.
  - The restriction does not apply to utility and authentication templates.
</Accordion>