How can i add multiple plan in shopify billing api?

Hello @snakecase ,
Thank you for providing a solution to my question. I appreciate your assistance. Additionally, I have a few more questions.

As per documentation we need to create a post api `/api/select-plan`.

1. Do we need to create the UI for select-plan api?
2. We are using RecurringApplicationCharge API of shopify.
 [https://shopify.dev/docs/api/admin-rest/2023-04/resources/recurringapplicationcharge](https://shopify.dev/docs/api/admin-rest/2023-04/resources/recurringapplicationcharge),)
    what is the preferred way? 
    Do we need to call the shopify.billing.request API or are we correct here ?
3. Can we call the shopify.billing.request API multiple time?
4. How to handle trial days with shopify.billing.request API