WordPress is not yet fully compatible with PHP 8.4. I would currently recommend using PHP 8.2. See: https://make.ww.wp.xz.cn/core/handbook/references/php-compatibility-and-wordpress-versions/
Unfortunately, many plugins and themes are also not yet compatible with PHP 8.4.
What exactly happens when you try to log in to the backend? Does an error message appear, and if so, which one?
I got my provider to roll back PHP to 7.4, I think. I have other sites that had the same issue, they returned to working order when the PHP was rolled back.
The site, reinstalled, that is causing problems does not show any warnings, it just does not allow login.
Thanks for your feedback. This is now a clean install. No plugins. Older version of PHP. So, no plugins to disable.
PHP 7.4 should no longer be used. As written above, PHP 8.2 is recommended.
However, it is strange if no login is possible. If no plugin is active, the cause can also be a security tool on the server or your browser. I once had a case where the hoster had suppressed HTTP referers. Then WordPress cannot perform a successful login.
Therefore, check the following:
- Can you log in with a different browser? Or on a completely different computer? An add-on in your browser or security tool on your computer could also be the reason.
- If this is not the case, I would recommend checking the developer console of your browser to see if there are any errors. There you should also see if the referrer is suppressed by your hoster. Alternatively, you could also place your project on a completely different hosting and see if it works there (which I assume it does).
That’s rough! The PHP 8.4 update likely broke plugin/theme compatibility. Ask your host to confirm or reset your WordPress login—also try the “Lost your password?” link.
Do you have FTP access to your host? Via FTP you’d try to enable WP debuging for providing us more details on your issue, post in here this thread any error/warning message you’ve got.
WordPress isn’t fully compatible with PHP 8.4 yet, so I recommend sticking with PHP 8.2 for now. Many plugins and themes may also break under 8.4. Can you share the exact error message you see when logging in?
