Add items to existing invoice via API

The docs aren’t clear as to whether or not you can add items to an already existing invoice via the API.

Is it possible?

Thanks in advance.

Yes, that should be possible if the invoice is a draft.

There isn’t an API endpoint to add a single invoice item, however you can first get the current array of invoice items (Get a single invoice), add your new invoice item to it, then update the invoice.