---
title: What does INVALID_SUB (Invalid User) mean?
description: "The **recipient number is invalid** - for example wrong format, too short/long, or not a valid mobile number. The message was not sent to this number. **What you can do:** Check number format (e.g. include country code, no spaces/letters). Clean your list…"
url: "https://www.smsgatewaycenter.com/blog/kb/what-does-invalid_sub-invalid-user-mean/"
updated: "2026-04-28"
category: "Bulk SMS / Errors & Error Codes"
---

# What does INVALID_SUB (Invalid User) mean?

The **recipient number is invalid** - for example wrong format, too short/long, or not a valid mobile number. The message was not sent to this number.

**What you can do:** Check number format (e.g. include country code, no spaces/letters). Clean your list to remove invalid entries.

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