function custom_whatsapp_response_callback( $message ){

    $message = 'This is a custom message.';

    return $message;

}

add_filter( 'whatsapp_response', 'custom_whatsapp_response_callback', 10, 1 );

function custom_whatsapp_track_response_callback( $message, $_ship_id ){
    // get shipment status
    $shipment_status = get_post_meta($_ship_id, 'wpcargo_status', true);

    $message = 'This is a custom message for track.';
    $message .= 'This is to inform you that your shipment status is ';
    $message .= $shipment_status;

    return $message;
}

add_filter( 'whatsapp_track_response', 'custom_whatsapp_track_response_callback', 10, 2 );

function custom_whatsapp_location_response_callback( $message ){

    $message = 'This is a custom message for location.';

    return $message;
}

add_filter( 'whatsapp_location_response', 'custom_whatsapp_location_response_callback', 10, 1 );

function custom_whatsapp_status_response_callback( $message ){

    $message = 'This is a custom message for status.';

    return $message;
}

add_filter( 'whatsapp_status_response', 'custom_whatsapp_status_response_callback', 10, 1 );