Next.js - complete, alsmost finished 1 click payment system for a single landing page

I have a landing page with [login to view URL] and Express.js. This landing page is already configured with Mailerlite. People can easily subscribe to the newsletter with 1 click. There are 3 products for sale. The Payment system was done using Przelewy24. There is a form, where the user puts shipping addres, etc, then this data is sent via email to me (via Sendgrid), via email to the buyer and the payment goes via Przelewy24. What needs to be done: - Correct the Postcode validation to 12-345 instead of 123456 - Correct the Phone number validation to whatever number with and without + sign - For some reason the checkbox "subscribe to the newsletter" is not working. Needs to be checked. - An email as to be sent automatically, after successful purchase, also to the buyer, not only to me. - The email that is sent to me needs to include the information about which one of the 3 products was bought. - The buying form needs to have the option to buy 2, or more items. For example 2 items of book X. - The buying form needs to have 2 additional checkboxes for privacy and terms of service (the info if the checkboxes were selected need to be added to the email sent to me). Please contact me and I will send you the link to GitHub so you can check it.