Fatal error: function wp_get_current_user()

Hi,

I installed Jetpack plugin but this errore occured:

Fatal error: Call to undefined function wp_get_current_user() in /home/suonarea/public_html/wp-includes/capabilities.php on line 1385

Any idea how to fix it? I can’t use it in this way

Thanks for helping

https://www.ads-software.com/plugins/jetpack/