---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/48003#article
headline: "48003: Callback returned an invalid response"
url: https://www.twilio.com/docs/api/errors/48003
inLanguage: en
dateModified: 2026-03-11T20:01:16.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 48003: Callback returned an invalid response

Log Type: APPLICATION

Log Level: ERROR

## Description

### Possible causes

* Your Frontline integration service returned a response which is invalid.
* Your service returned a response that was too large. Responses are capped at 64k.

### Possible solutions

* Make sure that callback returns a valid JSON which has the required fields that are defined in Frontline Docs.
* Make sure that your response size is less than 64k.