Using the Downpay API, you can add or remove products to purchase options with a single API call. For inputs, you will need:
- The id of the purchase option in the app. You can find this ID by editing the relevant purchase option in the app - it is the last part of the URL of the edit page
- The ids of the Shopify product(s) you'd like to add to the option.
The API is in GraphQL.