How do I send an image or file to an API

What's best practice to send an image or pdf to an API endpoint?

Scenario:
I have a vuejs app I want to send an image or PDF to a Rails api application. The I want to use active storage to organise the file in S3.

• Should I just post straight to S3 and somehow get rails to save to active storage?
• Or should I convert to BASE64 then send in body (seems a lil hacky)
• Create a POST request to the API server which accepts CORS rule (I always have trouble doing stuff like this for some reason)