Add variant to cart using API/custom app?

[pellsoft]

Is it possible to add a variant to a cart (using cart ID?) through a custom app? Or does this have to be done with the AJAX api through the theme?

I'm trying to develop a middleware that receives webhooks when a cart is created, and automatically adds a warranty variant to the cart. There's a lot of conflicting information regarding what's possible on this. Thanks!

[PaulNewton]

No. There is no backend api to communicate what's in a cart only frontend javascript pinging your app.

Use scripttags to add the item to the cart using the fronted ajax api

To create a custom order with specific items on the backend use draft orders.