The issue is because the WordPress ajax handler is not possible to reach, it gives a 403 error.
You can test it by visiting this URL: https://www.meditec.at/wp-admin/admin-ajax.php
This page should print '-1' by default. If there is an error message, it means that something is not right.
– There might be a malfunctioning .htaccess rule in the .htaccess file. Try reverting it back to the default, and see if it changes anything. This is the most likely cause.
– If the wp-admin/admin-ajax.php does not have correct permissions, the server may not allow opening it. Make sure to check the permissions of that file.
– If there is any filewall/malware protection, make sure that it does not block this file.
Once this ajax handler can be reached, the plugin should start working again normally.Best,
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