Custom Filter doesn’t work

I’m using the wp event manager plugin on WordPress and I’m trying to custom it. I created some custom fields in the back-end _event_modalita_erogazione. This field was compiled in every event created in the back-end.

I added the code for a new filter in the functions.php file as the official guideline.

// ADD FILTER
/**
 * Adding via filter or you can directly add in a template file
 */
add_action( 'event_manager_event_filters_search_events_end', 'filter_by_modalita_erogazione_field' );
function filter_by_modalita_erogazione_field() { ?>

<div class="wpem-row">
    <div class="wpem-col">
        <div class="wpem-form-group">
                <div class="search_event_types">
                <label for="search_event_types" class="wpem-form-label"><?php _e( 'Erogazione', 'event_manager' ); ?></label>
                <select name="filter_by_erogazione" class="event-manager-filter">
                    <option value=""><?php _e( 'Erogazione', 'event_manager' ); ?></option>
                    <option value="aula"><?php _e( 'Aula', 'event_manager' ); ?></option>
                    <option value="videoconferanza"><?php _e( 'Videoconferenza', 'event_manager' ); ?></option>
                    <option value="e-learning"><?php _e( 'E-learning', 'event_manager' ); ?></option>
                </select>
            </div>
        </div>
    </div>
    </div>
<?php
}

/**
 * This code gets your posted field and modifies the event search query
 */
add_filter( 'event_manager_get_listings', 'filter_by_state_field_query_args', 10, 2 );
function filter_by_state_field_query_args( $query_args, $args ) {
    if ( isset( $_POST['form_data'] ) ) {
        parse_str( $_POST['form_data'], $form_data );
        // If this is set, we are filtering by modalita erogazione.
        if ( ! empty( $form_data['filter_by_erogazione'] ) ) {
            $event_modalita_erogazione = sanitize_text_field( $form_data['filter_by_erogazione'] );
            var_dump( $event_modalita_erogazione );
            $query_args['meta_query'][] = array(
                'key'     => '_modalita_erogazione',
                'value'   => $event_modalita_erogazione,
            );
        }
    }
    var_dump( $query_args );
    return $query_args;
}

I added on the back-end the input field:

Etichetta Tipo Placeholder / Opzioni Meta Key
Modalità di erogazione multiple selection aula videoconferenza e-learning _event_modalita_erogazione

and in the DB I have the association of the event with this data, 8 row in total

| meta key| data | |:—- |:——:| | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} | | _event_modalita_erogazione | a:2:{i:0;s:4:”aula”;i:1;s:15:”videoconferenza”;} |

but when I tried to use the filter and select “Erogazione->Videoconferenza” the page reported to me “no elements found”.

The debug print is

string(15) "videoconferanza" array(13) { ["post_type"]=> string(13) "event_listing" ["post_status"]=> string(7) "publish" ["ignore_sticky_posts"]=> int(1) ["offset"]=> int(0) ["posts_per_page"]=> int(10) ["orderby"]=> string(10) "meta_value" ["order"]=> string(3) "ASC" ["tax_query"]=> array(0) { } ["meta_query"]=> array(1) { [0]=> array(2) { ["key"]=> string(20) "_modalita_erogazione" ["value"]=> string(15) "videoconferanza" } } ["update_post_term_cache"]=> bool(false) ["update_post_meta_cache"]=> bool(false) ["cache_results"]=> bool(false) ["fields"]=> string(3) "all" }

The page I need help with: [log in to see the link]