Error Updating / activating plugin

First I tried to update the plugin which ended up in an HTTP ERROR 500 for al the website. I deleted the plugin and installed it again, but when I try to activate it I get the following error: Parse error: syntax error, unexpected ‘[‘ in /var/www/html/SITE FOLDER/wp-content/plugins/onesignal-free-web-push-notifications/onesignal-admin.php on line 962.

Need help please! Thank you. Take care. Sebastian