POST fail, error #400, Bad HTTP “Content-Type” header

In your screenshot, you're setting your Content-Type header to "text/json". The error message is indicating that only "application/octet-stream" or "text/plain; charset=dropbox-cors-hack" are accepted.

Thank you for your quick reply!

as I wrote in my msg, I've tried all possible "Content-Type" without any success including "application/octet-stream" or "text/plain; charset=dropbox-cors-hack"

Can you share screenshots for those attempts then?

sure, different REST client using Firefox:

The response includes the Content-Type header that the API received. In both of these additional cases, it seems "; charset=UTF-8" was appended to the Content-Type you specified, resulting in an invalid Content-Type. Firefox is known to do this.

I posted an answer here about Firefox's behavior, including some information on ways to do this properly:

https://stackoverflow.com/questions/33902289/using-dropbox-v2-api-from-browser

Thank you, since its 3AM here I'm off to sleep now so I'll dive into it tomorrow, many thanks for your support!!!

Dear Gregory,

I've used a standalone REST client instead of the browsers add ins and this works as it should, once again, thank you for your support!

Best,

R.