Dropbox API, I can't upload a file to Dropbox (err. 401 Unauthorized)

Question

Please, help: I can't upload a file to Dropbox (err. 401 Unauthorized)

I am using Delphi XE3, Indy THttp component. Please, can you look at the header and body of the message being sent to see if there is an error?
I got AccessToken on
https://dropbox.github.io/dropbox-api-v2-explorer/#auth_token/from_oauth1 
I assume it's persistent and I don't need to retrieve it every time I access it

const
API_URL = 'https://content.dropboxapi.com/2/files/upload';
cFile = 'D:\my_file_path_on_pc	estfile.txt';
cook
wAccessToken : string;
Source: TFileStream;
IdHTTP: TIdHTTP;
Res, OpenSSLpath, wVal : string;
Ssl: TIdSSLIOHandlerSocketOpenSSL;
begin
wAccessToken := '_my_access_token_';
Source := TFileStream.Create(cFile, fmOpenRead);
...
...
IdHTTP.Request.CustomHeaders.Values['Authorization'] := 'Bearer ' + wAccessToken;
IdHTTP.Request.CustomHeaders.Values['Dropbox-API-Arg'] :=
'{ "autorename": false, "mode": "add", "mute": false, "path": "/CUZK/test.txt", "strict_conflict": false }';
IdHTTP.Request.CustomHeaders.Values['Content-Type'] := 'application/octet-stream';

Res := IdHTTP.Post(API_URL, Source);

Greg-DB · Accepted Answer

@Polas Здравко is correct; new Dropbox access tokens are not persistent. Dropbox is no longer offering the option for creating new long-lived access tokens. Dropbox is switching to only issuing short-lived access tokens (and optional refresh tokens) instead of long-lived access tokens. You can find more information on this migration here.

Apps can still get long-term access by requesting "offline" access though, in which case the app receives a "refresh token" that can be used to retrieve new short-lived access tokens as needed, without further manual user intervention. You can find more information in the OAuth Guide and authorization documentation. There's a basic outline of processing this flow in this blog post which may serve as a useful example.

And for debugging issues like this, you should print out the HTTPS response body, as it should contain a more useful error message (such as 'invalid_access_token' or 'expired_access_token'). You may need to refer to the documentation for your network client for information on how to access the response body.