This FAQ applies to you if you are seeing an error that looks like this:
Call to undefined method MaxMind\Db\Reader::getWithPrefixLen() in vendor/geoip2/geoip2/src/Database/Reader.php
If that’s the case, please check if you have maybe the MaxMind PHP C extension installed.
If you don’t know if that’s the case, you can execute the command
php -i on the command line and look if the MaxMind extension is installed. To solve this problem you will need to disable this extension and restart your webserver. If you don’t know how to do this, we recommend contacting your system administrator or your hoster.
Matomo for WordPress
If you are using Matomo for WordPress there’s also a chance that a different plugin bundles an older (unsupported) version of the MaxMind. In this case you could try disabling other plugins to see if this fixes the issue. In such a case please create an issue in our issue tracker and let us know which plugin is causing this issue. If you don’t know which plugin is causing this error you can also instead post your Matomo for WordPress system report in a new issue and we will try to reproduce it.