After installing Accordion I try to activate it but it fails with the following message:
Plugin could not be activated because it triggered a fatal error.
Fatal error: Can't use method return value in write context in /data/17/1/142/147/1631310/user/1758433/htdocs/sos/sos/wp-content/plugins/accordions/includes/class-WPAdminSettings.php on line 657
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This is probably old version PHP issue on your server, can you please use update version of PHP and see what's happening?