Sell vouchercode in 1 plugin and redeem vouchercode in another plugin AGENDA

Hello everyone!
My first topic here.

My client have a special request as described below.
Which plugins can I use? And how to connect both databases?
Or combine it with another plugin?

Or does some one have a better idea to realize this special request?

This is the request:

  1. Purchase of the deal:
    I want to sell 3 different sushi boxes as a ‘super deal’ for a period of 3 months. Box A, B and C. Each box has a different price. When purchasing, the customer must enter name, telephone number and email address. After a period of 3 months I want to sell other boxes: Box D, E and F.

  2. Voucher code
    a. After this purchase, the customer + seller must receive a confirmation by e-mail with a unique voucher code consisting of 12 characters.
    b. The voucher code may only contain numbers and letters. Preferably not the numbers 1 and 0. And not the letters O, I, L. This to avoid confusion when entering.
    c. Preferably, the 12-digit code consists of this format XXXX-XXXX-XXXX (so that it can be entered and listed easily and quickly).
    d. Each voucher code must be valid for 6 months (or 180 days) from date of purchase. During this period, the customer can decide for himself when to redeem the voucher code. After 6 months, the voucher code may no longer be exchanged.
    e. If the seller cancels the deal at the customer’s request within 14 days of purchase, the voucher code should also expire. The voucher code must then no longer be usable.

  3. Redeem in calendar
    a. Redemption of the voucher code must only be possible in an online agenda. Once an appointment has been made, the voucher code must be marked as used. Without a valid voucher code it should be impossible to schedule an appointment.
    b. In the online agenda, the customer must be able to choose time slots when making an appointment. Each time slot lasts 5 minutes. When choosing a date/time, the customer must enter the voucher code. The agenda must recognize the voucher code and state the short description of the chosen box. For example: ‘Sushi box A’.
    c. If you schedule an appointment before 12 noon, you can choose a time slot that same day (or later). If you try to schedule an appointment after 12:00, this is only possible for the next day (or later).

These are the opening times;
Monday: closed
Tuesday: 16:00-21:30
Wednesday: 16:00-21:30
Thursday: 16:00-21:30
Friday: 16:00-21:30
Saturday: 16:00-21:30
Sunday: 16:00-21:30

If the system recognizes an invalid voucher code, it should be impossible to schedule an appointment for the customer. A warning should then apply: “This voucher code is no longer valid. Please enter a valid voucher code.”