Upload attachment using rest API

[MartinHBramwell]

[solved] cURL example of an attachment upload RPC call?

I need to use the RPC API to attach a few files to a specified Sales Invoice. I would be most grateful if somone could point me to a worked through and working example of how that is done? I’m using: ERPNext: v12.7.1 (version-12) Frappe Framework: v12.5.1 (version-12) Description: Ubuntu 18.04.4 LTS Codename: bionic