ssl problem

whenever i try to install SSL i see this error

Fatal error: Uncaught Error: Call to undefined function dns_get_record() in /www/wwwroot/affiliateara.com/wp-content/plugins/really-simple-ssl/lets-encrypt/class-letsencrypt-handler.php:508 Stack trace: #0 /www/wwwroot/affiliateara.com/wp-content/plugins/really-simple-ssl/lets-encrypt/class-letsencrypt-handler.php(65): rsssl_letsencrypt_handler->verify_dns() #1 /www/wwwroot/affiliateara.com/wp-content/plugins/really-simple-ssl/lets-encrypt/letsencrypt.php(76): rsssl_letsencrypt_handler->__construct() #2 /www/wwwroot/affiliateara.com/wp-content/plugins/really-simple-ssl/lets-encrypt/letsencrypt.php(113): RSSSL_LETSENCRYPT::instance() #3 /www/wwwroot/affiliateara.com/wp-includes/class-wp-hook.php(303): RSSSL_LE() #4 /www/wwwroot/affiliateara.com/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters() #5 /www/wwwroot/affiliateara.com/wp-includes/plugin.php(470): WP_Hook->do_action() #6 /www/wwwroot/affiliateara.com/wp-settings.php(441): do_action() #7 /www/wwwroot/affiliateara.com/wp-config.php(89): require_once(‘/www/w in /www/wwwroot/affiliateara.com/wp-content/plugins/really-simple-ssl/lets-encrypt/class-letsencrypt-handler.php on line 508

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