Hey @vincentdev25, thanks for getting in touch! At the moment, there's no explicit way to download an invoice directly through the API, but you could use the API to get most of the information that is present in an invoice.
The easiest way to do this would be through the GraphQL order object (info on that here). Using the GraphQL object, you can query order related information like the total amount paid, the line items present in the order, relevant customer information and quite a bit more. I do know of some merchants and developers who use the order/orders resource to create customized invoices by leverage the data present via the API.
Hope this helps - let us know if we can clarify anything on our end.
