Hi, I have bought WP Travel Instamojo Checkout plugin and installed in my website (http://www.jollydaytours.com/), after plugin activation my site is not working and it showing White screen.
When I put debug to true and checked it displayed

Notice: Use of undefined constant ‘after_setup_theme’ – assumed ‘‘after_setup_theme’’ in /home/hxs4a8glxiw0/public_html/wp-includes/functions.php on line 5678

Notice: Use of undefined constant ‘remove_admin_bar’ – assumed ‘‘remove_admin_bar’’ in /home/hxs4a8glxiw0/public_html/wp-includes/functions.php on line 5678

Notice: Undefined variable: itineraries in /home/hxs4a8glxiw0/public_html/wp-content/plugins/wp-travel/inc/helpers.php on line 642

Fatal error: Uncaught Error: Call to undefined function wp_travel_is_checkout_page() in /home/hxs4a8glxiw0/public_html/wp-content/plugins/wp-travel-instamojo-checkout/wp-travel-instamojo-checkout.php:395 Stack trace: #0 /home/hxs4a8glxiw0/public_html/wp-includes/class-wp-hook.php(298): Wp_Travel_Instamojo_Checkout->enqueue(”) #1 /home/hxs4a8glxiw0/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array) #2 /home/hxs4a8glxiw0/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /home/hxs4a8glxiw0/public_html/wp-includes/script-loader.php(1300): do_action(‘wp_enqueue_scri…’) #4 /home/hxs4a8glxiw0/public_html/wp-includes/class-wp-hook.php(298): wp_enqueue_scripts(”) #5 /home/hxs4a8glxiw0/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters(NULL, Array) #6 /home/hxs4a8glxiw0/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #7 /home/hxs4a8glxiw0/public_html/wp-includes/general-template.php(2589): do_action(‘wp_head’) #8 /home/hxs4a8glxiw0/publi in /home/hxs4a8glxiw0/public_html/wp-content/plugins/wp-travel-instamojo-checkout/wp-travel-instamojo-checkout.php on line 395

Please help me fix this issue. I can provide admin details if needed.
Thank You