Fix Redsys Payment & Implement Subscriptions

I need assistance with my WooCommerce setup. The Redsys payment method is causing a critical error during the payment process in sandbox mode. Additionally, I need to implement a subscription function that allows both registered users and admins to manage and cancel subscriptions.

Key Requirements:
- Diagnose and fix the critical error with the Redsys payment method.
- Implement a subscription functionality within WooCommerce.
- Ensure the subscription function allows for easy management and cancellation for both users and admins.

Ideal Skills:
- Proficient in WooCommerce and WordPress.
- Experience with Redsys payment integration.
- Prior work with implementing WooCommerce subscription functionalities.
- Strong problem-solving skills to troubleshoot and rectify payment processing errors.