fatal error when activating really simple ssl

I have support access on for aficreditsolutions.com. I received this error when activating really simple SSL.

Fatal error: Uncaught Error: Call to a member function flush_rules() on null in /home/agelafin/public_html/aficreditsolutions.com/wp-includes/rewrite.php:273 Stack trace: #0 /home/agelafin/public_html/aficreditsolutions.com/wp-admin/includes/misc.php(469): flush_rewrite_rules() #1 /home/agelafin/public_html/aficreditsolutions.com/wp-includes/class-wp-hook.php(288): update_home_siteurl('http://aficredi…', 'https://aficred…':wink: #2 /home/agelafin/public_html/aficreditsolutions.com/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array) #3 /home/agelafin/public_html/aficreditsolutions.com/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #4 /home/agelafin/public_html/aficreditsolutions.com/wp-includes/option.php(401): do_action('update_option_s…', 'http://aficredi…', 'https://aficred…', 'siteurl':wink: #5 /home/agelafin/public_html/aficreditsolutions.com/wp-content/plugins/really-simple-ssl/class-admin.php(1064): update_option('siteurl', 'https://aficred…':wink: #6 /home/agelafin/public_html/aficreditsoluti in /home/agelafin/public_html/aficreditsolutions.com/wp-includes/rewrite.php on line 273