Fatal error: Uncaught Error: Call to undefined function

Dear, i am getting this error when i am using search bar to search a product
this is the link
https://curix.com.pk/?s=panad&post_type=product&dgwt_wcas=1

Fatal error: Uncaught Error: Call to undefined function DgoraWcas\Engines\WordPressNative\json_last_error() in /home/curixcom/public_html/wp-content/plugins/ajax-search-for-woocommerce/includes/Engines/WordPressNative/Search.php:615 Stack trace: #0 /home/curixcom/public_html/wp-includes/class-wp-hook.php(286): DgoraWcas\Engines\WordPressNative\Search->overwriteSearchPage(Object(WP_Query)) #1 /home/curixcom/public_html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array) #2 /home/curixcom/public_html/wp-includes/plugin.php(531): WP_Hook->do_action(Array) #3 /home/curixcom/public_html/wp-includes/class-wp-query.php(1753): do_action_ref_array(‘pre_get_posts’, Array) #4 /home/curixcom/public_html/wp-includes/class-wp-query.php(3404): WP_Query->get_posts() #5 /home/curixcom/public_html/wp-includes/class-wp.php(622): WP_Query->query(Array) #6 /home/curixcom/public_html/wp-includes/class-wp.php(739): WP->query_posts() #7 /home/curixcom/public_html/wp-includes/functions.php(1105): WP->main(”) #8 /home/curixcom in /home/curixcom/public_html/wp-content/plugins/ajax-search-for-woocommerce/includes/Engines/WordPressNative/Search.php on line 615

When i remove the search string from the link then it works fine.
https://curix.com.pk/?s=&post_type=product&dgwt_wcas=1

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