PHP fatal error V6 | WordPress.org

PHP Fatal error: Uncaught Error: Call to undefined function rsssl_wrap_htaccess() in /public_html/wp-content/plugins/really-simple-ssl/upgrade.php:148
Stack trace:
#0 /public_html/wp-includes/class-wp-hook.php(308): rsssl_upgrade(”)
#12 {main}
thrown in /home/dc1a155/public_html/wp-content/plugins/really-simple-ssl/upgrade.php on line 148

my headers are:

# Really Simple SSL
Header always set Strict-Transport-Security: "max-age=31536000" env=HTTPS
Header always set Content-Security-Policy "upgrade-insecure-requests;"
Header always set X-XSS-Protection "0; mode=block"
Header always set X-Content-Type-Options "nosniff"
Header always set Referrer-Policy "strict-origin-when-cross-origin"
Header always set X-Frame-Options: "SAMEORIGIN"
Header always set Permissions-Policy: "no-referrer-when-downgrade"
Header always set Expect-CT "max-age=7776000, enforce"
# End Really Simple SSL

Any idea if the error is serious to solve it ?