Hello. We recently needed to upload bitstreams through REST API. We used following call:
{server-url}/server/api/core/bundles/ab01bfb5-a078-4e60-895f-50a71f1a3cb1/bitstreams
Please note that the UUID of the call is UUID of the Bundle, not the Item.
We sent file in body in form-data. Key "properties" contains JSON with necessary metadata
and key "file" contains file.
Since you state you worked with other APIs, I don't think it would be helpful to
add information about tokens and authentication.
I hope this can help you.
Best regards,
Majo