WooCommerce Subscriptions & Bookings Customization: Two Client Stories

function my_process_gateway_event( array $event ): void {
    // Atomic insert — survives concurrent requests and cache misses.
    global $wpdb;
    $inserted = $wpdb->query( $wpdb->prepare(
        "INSERT IGNORE INTO {$wpdb->prefix}gateway_events (event_id, created_at)
         VALUES (%s, %s)",
        $event['id'], current_time( 'mysql', true )
    ) );

    if ( ! $inserted ) {
        return; // already seen — safe to return 200 to the gateway
    }

    // ... process the event; if it fails, delete the row so retry can work.
}

wp_cache_add is not atomic under the default object cache. For webhooks, use a DB unique index — it's the only reliable mutex across PHP workers.

add_filter( 'wcs_subscription_plan_switch_payment_required', function ( $payment_required, $subscription, $new_plan ) {
    $last = (int) $subscription->get_meta( '_free_switch_at' );
    if ( ! $last || ( time() - $last ) > 90 * DAY_IN_SECONDS ) {
        $subscription->update_meta_data( '_free_switch_at', time() );
        $subscription->save();
        return false; // waive prorated charge
    }
    return $payment_required;
}, 10, 3 );

Test against trials, sign-up fees, and mid-cycle switches.

function my_local_to_utc( string $local, string $tz ): DateTimeImmutable {
    return ( new DateTimeImmutable( $local, new DateTimeZone( $tz ) ) )
        ->setTimezone( new DateTimeZone( 'UTC' ) );
}

Store UTC, display local, never compare a "local" string to a UTC timestamp — this was the root cause of the DST double-booking bug.