Complete Codex Registration Guide: From Account Creation to Phone Verification

Introduction

Codex (OpenAI's AI programming assistant) has been gaining momentum recently, but many developers find themselves stuck at the most basic step — account registration. Reading through countless tutorials only to fail at creating an account is more common than you'd think. This article walks through the complete Codex registration process, highlighting the key pitfalls to avoid, so you can get registered and start using it without hassle.

OpenAI Codex is an AI tool built on GPT large language models, specifically optimized for code generation and programming assistance. It was originally known as the underlying engine powering GitHub Copilot, capable of understanding natural language descriptions and generating corresponding code snippets. In 2025, OpenAI launched Codex as a standalone product with enhanced code comprehension, debugging, and refactoring capabilities, supporting autonomous multi-step programming tasks in sandboxed environments. Codex shares its account system with ChatGPT — this is the fundamental reason why the registration process is closely tied to ChatGPT.

The Most Critical First Step: Don't Open Codex Directly

This is the first pitfall many people fall into, and it's the most fatal one — never register an account directly through the Codex software.

If you try to register directly through the Codex client or the ChatGPT plugin in VS Code, the system will invariably throw a "verification mismatch" error. This error leaves many newcomers confused, repeatedly trying but never getting through.

From a technical perspective, the Codex client's registration flow relies on the OAuth 2.0 authorization protocol to interact with ChatGPT's authentication server. When a user initiates registration from the Codex side, the client generates a local session token and attempts to sync with OpenAI's identity verification service. However, since the Codex client's registration interface isn't a complete account creation entry point but merely a login redirect page lacking the full account initialization flow, the token state becomes inconsistent with what the server expects, triggering the "verification mismatch" error. This is essentially an authentication state synchronization issue between client and server.

The correct approach is: complete your account registration on the ChatGPT website first, then return to Codex to log in. This order cannot be reversed.

Register an Account on the ChatGPT Website

Registration Process

1. Open the ChatGPT website and find the "Sign up free" button
2. Enter your email: Here's the good news — Chinese domestic email addresses are fully supported. Whether it's QQ Mail or 163 Mail, both work fine. You don't need to prepare a foreign email address
3. Verify your email: After submitting, check your inbox for the verification code and enter it on the registration page
4. Complete your profile: You can enter any name; age must be over 18
5. Finish creation: Click "Complete account creation"

The entire process is very straightforward. The key is to make sure this step is completed on the ChatGPT web interface, not within the Codex client.

Log into Codex with Your ChatGPT Account

Once your account is registered, you can open Codex to log in. Whether you're using:

• The standalone Codex client
• The ChatGPT plugin in VS Code

The process is the same:

1. Open the Codex software
2. Click "Continue with ChatGPT"
3. The system will automatically recognize your newly registered ChatGPT account
4. Click "Continue" to proceed to phone number verification

Following this order will prevent the "verification mismatch" error.

Phone Number Verification: Detailed Steps

Obtaining a Verification Number

Phone verification is the second major hurdle where many people get stuck. Since OpenAI has regional restrictions on phone numbers, Chinese domestic numbers cannot be used directly. You'll need to obtain a foreign number through a third-party SMS verification platform.

An SMS verification platform is an online service that provides temporary virtual phone numbers. It works by the platform holding bulk SIM cards from various countries or partnering with telecom carriers to obtain virtual number ranges. When a user rents a number, any SMS received by that number is forwarded in real-time via API to the platform's interface for the user to view. Common platforms include SMS-Activate, 5SIM, and others. Note that some numbers may have been used multiple times and flagged as high-risk by OpenAI, causing verification failure. In such cases, you'll need to switch to a new number. It's recommended to choose numbers labeled as "never used for OpenAI services" to improve your success rate.

Specific steps:

1. Obtain an available number from an SMS verification platform (US numbers are recommended)
2. Copy the number into Codex's verification page
3. Important: The country/region selection must match the actual number (e.g., select United States for a US number)
4. Click "Continue" to send the verification code
5. Return to the SMS platform to check the received code
6. Enter the verification code on the Codex page and click continue

Once verification passes, Codex is officially ready to use.

Common Errors and Solutions

During the actual process, you may encounter various errors. Here's a troubleshooting approach:

Retry Login

When you encounter an error, try logging in again 2-3 times. Often it's just temporary network fluctuation, and retrying a few times resolves it.

Clear Configuration Files

If you've previously configured third-party APIs, it's recommended to delete the related configuration files and reinstall the Codex client. Old configurations may conflict with the new account.

Network Environment Issues

If you consistently get a 403 error stating "region not supported," this is a network environment issue. OpenAI implements regional access restrictions based on IP geolocation. As of now, OpenAI's services are unavailable in mainland China, Russia, Iran, and certain other countries and regions. The system checks the user's IP address location to determine whether access is permitted, returning an HTTP 403 status code when detecting requests from restricted regions. This restriction involves compliance requirements, data privacy regulations, and export controls among other factors. The 403 error code in HTTP protocol means "the server understands the request but refuses to fulfill it" — unlike 404 (not found), it explicitly indicates that access is actively denied. If you encounter this issue, you need to ensure your network environment meets the requirements. This is something users need to resolve on their own.

Summary

The entire Codex registration process can be summarized in three steps:

1. Register an account on the ChatGPT website first (don't register directly in Codex)
2. Log into Codex with your registered account
3. Complete phone verification through an SMS verification platform

As long as you strictly follow this order and avoid the biggest pitfall of "registering directly in Codex," most people can complete registration smoothly. When encountering errors, troubleshoot step by step following the "retry → clear configuration → check network" approach, and most issues can be resolved.

Key Takeaways

• Never register directly in the Codex client; you must complete registration on the ChatGPT website first, then log into Codex
• Chinese domestic email addresses (QQ Mail, 163 Mail) can be used to register ChatGPT accounts
• Phone verification requires obtaining a foreign number through a third-party SMS verification platform; US numbers are recommended
• A 403 error indicating region mismatch is a network environment issue; ensure your access origin meets OpenAI's regional requirements
• When encountering errors, troubleshoot in this order: retry login → delete config files and reinstall → check network environment