Your 'MediaType' attribute value is incorrect. According to your screenshot, you've specified it as 'form-data' - but this isn't a valid value.
Replace 'form-data' with 'application/x-www-form-urlencoded'. The MediaType dropdown generates the 'Content-Type' HTTP header value in your request
Also - in your payload you have included HTTP headers (Content-Type, Content-Transfer-Encoding, 'Content-Disposition) - you shouldn't be specifying these in the payload.
Also - it looks like you're setting the boundaries yourself in the payload - if setup correct, these are dynamically generated. You should include JUST the payload and nothing else.
Hope this helps!
if this helped answer the post, could you please mark it as 'solved'? Also if you consider whether the title of your post is relevant? Perhaps if the post is solved, it might make sense to update the Subject header field of the post to something more descriptive? This will help people when searching for problems. Ta