Troubleshooting common TYPO3 backend login problems

The following errors can happen during backend login:

Login page reloads without error

Try deleting all browser cookies and caches or use a different browser / device. There might be an outdated cookie that prevents log-in.
Clear all TYPO3 caches via console command or install tool.
Delete folder var/cache to remove possible corrupted cache data.
Check the cookies configuration in TYPO3: Ensure that cookie-related settings (sessionTimeout, cookieDomain) are correct and not causing session issues.

"Invalid Credentials" error

Check if the username and password are correct.
Try to create a new administrative user and use that one.

White screen before or after login

Many older TYPO3 files contain a line like the following that needs to be replaced:

-defined('TYPO3_MODE') or die();
+defined('TYPO3') or die();

The PHP constant TYPO3_MODE was removed with TYPO3 v12 but it is still widespread in older code examples and extensions. This can also happen if you installed a TYPO3 extension that is not compatible with newer TYPO3 versions.

If you have this line in your own code, replace it. If you find it in the above code in a third party extension, check if a newer version is available. If you do not find one you can try to reach out to the extension author or patch it yourself.

Access denied before or after login

If the line above contains "Access denied." or a similar string that string will be output and the login page contains nothing else:
```
-defined('TYPO3_MODE') or die('Access denied.');
+defined('TYPO3') or die('Access denied.');
```
Copied!
The solution is the same like for White screen before or after login.
Check file permissions on the TYPO3 files.
Check the .htaccess or Nginx configurations

"Account locked" message

Wait the required time
Or delete the folder var/cache

"Page Not Found" or 404 Error

Check file permissions on the TYPO3 files.
Check the .htaccess or Nginx configurations

Broken login form or missing elements

Try deleting all browser cookies and caches or use a different browser / device. There might be an outdated cookie that prevents log-in.
Clear all TYPO3 caches via console command or install tool.
Was there a warning during composer install? The _assets folder might not have been properly symlinked during installation.
Check the browser console for errors.