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15:57 25 Jul 2026

Telegram API Authentication Fails with 401 Unauthorized in Python Despite Successful Login

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I am developing a Python application that uses the Telegram API to automate messaging and manage Telegram accounts. My goal is to send automated notifications and interact with Telegram users after specific events occur in my application.

I carefully followed the official Telegram API documentation and completed the following steps:

  • Created a Telegram application.

  • Obtained the API ID and API Hash.

  • Installed the required Python libraries.

  • Implemented the authentication flow.

  • Successfully logged in using my phone number.

  • Received the verification code.

  • Generated the session file.

The authentication process appears to complete successfully. The application logs in without any errors, and the session is created correctly.

However, when I try to perform API requests, I consistently receive the following error:

401 Unauthorized

Request failed due to invalid authentication credentials.

The simplified version of my code is:

client.send_message(
    entity="@example",
    message="Test message"
)

I have already tried the following:

  • Deleted the existing session file and logged in again.

  • Generated a new API ID and API Hash.

  • Verified that my Telegram account is active.

  • Updated all Telegram Python libraries to the latest version.

  • Tested using a new Telegram account.

  • Confirmed that the API credentials are correct.

I also confirmed that:

  • The API ID is valid.

  • The API Hash is correct.

  • Login completes successfully.

  • No exceptions occur during authentication.

  • A valid session file is created.

Despite these checks, every API request returns a 401 Unauthorized error.

Development Environment

  • Python: 3.12

  • Operating System: Windows 11

  • Library: Latest Telegram Python client

  • Authentication: API ID + API Hash + Session

My Questions

  1. What are the most common reasons for receiving a 401 Unauthorized error after successful authentication?

  2. Could this issue be related to session files or API credentials?

  3. Should I generate a new API ID and API Hash or create a new Telegram application?

  4. What debugging steps are recommended to determine whether the problem is related to authentication, session management, or API configuration?

Any suggestions or explanations would be greatly appreciated. I have reviewed the official documentation several times but have not been able to identify the cause of the issue.

Thank you for your time and assistance.

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