Uncaught Error: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method Swelltek_Content_Base::handle_opening_div() cannot be called statically
in /var/www/swelltek/live/wp-includes/class-wp-hook.php on line 324

Call stack:

1. WP_Hook::apply_filters()
   wp-includes/class-wp-hook.php:348
2. WP_Hook::do_action()
   wp-includes/plugin.php:517
3. do_action()
   wp-content/themes/swelltek_alpha/woocommerce/content-single-product.php:60
4. require('/var/www/swelltek/li...t-single-product.php')
   wp-includes/template.php:812
5. load_template()
   wp-content/plugins/woocommerce/includes/wc-core-functions.php:285
6. wc_get_template_part()
   wp-content/plugins/woocommerce/includes/wc-template-functions.php:1002
7. woocommerce_content()
   wp-content/themes/swelltek_alpha/woocommerce.php:9
8. include('/var/www/swelltek/li...lpha/woocommerce.php')
   wp-includes/template-loader.php:106
9. require_once('/var/www/swelltek/li.../template-loader.php')
   wp-blog-header.php:19
10. require('/var/www/swelltek/live/wp-blog-header.php')
    index.php:17