Trying to update repeater field (ACF) dynamically with data from Contact Forms 7

I'm trying to feed a repeater field with the values submitted via a registration form (I'm using Contact Forms 7).

When debugging the array of values passed to the add_row function, everything seems to be well introduced, but there must be an error because nothing happens, and the repeater is not updated. Actually, the function add_row seems to return false, but I cannot find the error...

So far this is the code that I'm using:

add_action( 'wpcf7_before_send_mail', 'mafsuf_wpcf7_update_repeater_field' );
function mafsuf_wpcf7_update_repeater_field($wpcf7) {
 
        //Data sent by WPCF7
        $submission = WPCF7_Submission::get_instance();
        
        //Get post ID
        $event_post_id = $submission-get_meta( 'container_post_id' );

        //Get other values
        $data = $submission-get_posted_data();
        $asist_date = date('Ymd');
        $asist_org = $data['ev_soci_id'];
        $asist_name = $data['ev_nom'] . ' ' . $data['ev_cognoms'];
        $asist_notes = $data['ev_carrec'];

        //ADD ROW TO REPEATER FIELD BY KEY
        //field_61704a5a97d56 is the repeater's field key assistance_list
        $field_key = 'field_61704a5a97d56';
        $row = array(
            'field_61704bb597d57' = $asist_date,   //'asist_date'
            'field_61704d4597d59' = $asist_org,    //'asist_org'
            'field_61704cd797d58' = $asist_name,   //'asist_name'
            'field_61704e4297d5a' = $asist_notes,  //'asist_notes'
        );
        
        add_row( $field_key, $row, $event_post_id );

        //For DEBUG Purposes
        error_log(print_r($row,true),3,__DIR__./../log.txt);
        //When checking the log file I confirm that $row has the correct format

        //Not sure that return is necessary because we are not changing $wpcf7 at all
        return $wpcf7;
        
}

Any thoughts? Thanks!