Q:

Dropbox download file API stopped working with 400 error

I use dropbox download file API , and i got a token , but  it's return 400 bad request error 
"Error in call to API function "files/download": Must provide HTTP header "Authorization" or URL parameter "authorization"
I follow dropbox api doc , but it cannot work ~""~
How do I fix it ? 
this is my code ( angular2 )
downloadFile(fileid){
let headers = new Headers();

headers.append('Authorization', 'Bearer ' + this.accessToken);
headers.append('Dropbox-API-Arg','path:'+ fileid);

return this.http.post('https://content.dropboxapi.com/2/files/download',new RequestOptions({ headers: headers ,responseType:ResponseContentType.ArrayBuffer})).map((res) => {

  let arrayBuffer = res.arrayBuffer();
  let contentType = res.headers.get('content-type');
  return {
    fileid: fileid,
    blob: new Blob([arrayBuffer], { type: contentType })
  };
});

A:

I use dropbox v2 api in android. Just as you, I got 400 bad request. It turns out that Android HttpUrlConnection set a default "Content-Type" header value. And dropbox download api require "Content-Type" to be missing or empty. I don't have same issue in iOS though.
So maybe in angular2, you need to do something like:
headers.append('Content-Type','');

Also the 'Dropbox-API-Arg' header need to be like:
headers.append('Dropbox-API-Arg','{\"path\": \"/filepath\"}');

