Get new AccessToken when access token expired (Android)

I apologize in advance for my English.

I have several android applications that use Dropbox to send and load data. 

Until the last update, Dropbox communication worked properly - probably an Access Token without expiring

 

Here is a sample of the code I use:

// Create Dropbox client
DbxRequestConfig config;
config = new DbxRequestConfig("dropbox/appName");
return new DbxClientV2(config, ACCESS_TOKEN);

// save Access Token
if (ACCESS_TOKEN == null) {
    String accessToken = Auth.getOAuth2Token(); //generate Access Token
    if (accessToken != null) {
        //add accessToken to SharedPreferences
        SharedPreferences prefs = context.getSharedPreferences("com.appName.dropboxintegration", Context.MODE_PRIVATE);
        prefs.edit().putString("access-token", accessToken).apply();
    }
}

//load Acces token from SharedPreferences
SharedPreferences prefs = context.getSharedPreferences("com.appName.dropboxintegration", Context.MODE_PRIVATE);
String accessToken = prefs.getString("access-token", null);
if (accessToken == null) {
    Log.d("AccessToken Status", "No token found");
    return null;
} else {
    //accessToken already exists
    Log.d("AccessToken Status", "Token exists");
    return accessToken;
}

 

// here it falls on expired
try {
    MoveFile();
} catch (InvalidAccessTokenException ex) {
    endSend = null;
    resetToken = true;
    ex.printStackTrace();
} catch (DbxException e) {
    endSend = null;
    e.printStackTrace();
}

I tried to call OAuth again. - repeatedly reports the token has expired

I tried to terminate the token - it won't work

I tried to use Auth.startOAuth2PKCE () to log in - it reports a token malfunction

Auth.getOAuth2Token () does not return a new token

 

my questions:

How do I request a new AccessToken whenever I find out it's expired.

I can somehow request a token without expiring.

Do I need to convert the application to a short-term token?