Access Token Can't be refreshed without refresh token and app key in Python

I see you are using the official Dropbox Python SDK to do the upload work, but are attempting to perform the refresh process yourself using 'requests' to call the /oauth2/token endpoint directly. The official Dropbox Python SDK can handle the refresh process for you automatically though, and I strongly recommend having it do so instead of attempting to implement the refresh process yourself. You can see an example of supplying the credentials to the Dropbox object here, in which case it will handle the refresh for you automatically.

Yes, but it is just setup nothing related to token refresh. basically, my software stopped after 4 hours first it showed the error of an expired access token. So, I used this method by searching. Can you please point out the corrections in my code?

In order to get this working, please set up the client by supplying the refresh token, etc., to it directly, as shown in the example, so that it can perform the refresh process for you. That way, it can continue performing API calls successfully for more than four hours.

So flow like this? It still shows an error. 

import sys
import dropbox
import time
from dropbox import DropboxOAuth2FlowNoRedirect
from dropbox.files import WriteMode

while True:
    with dropbox.Dropbox(oauth2_access_token='access token',
                     oauth2_access_token_expiration=expiry,
                     oauth2_refresh_token='refresh token',
                     app_key='app key',
                     app_secret='secret'):
        try:
            with open('rtk.txt', 'rb') as f:
                file_contents = f.read()   
            dbx.files_upload(file_contents, '/rtk.txt', mode=dropbox.files.WriteMode('overwrite'))
        except Exception as e:
            print(f"An error occurred: {e}")
    time.sleep(60)

 Error: An error occurred: name 'dbx' is not defined

That error indicates that you're attempting to use an object that isn't defined. Since you're trying to access a client with the name "dbx", add "as dbx" at the end of the "with" statement (before the ":"), like this:

    with dropbox.Dropbox(oauth2_access_token='access token',
                     oauth2_access_token_expiration=expiry,
                     oauth2_refresh_token='refresh token',
                     app_key='app key',
                     app_secret='secret') as dbx:

 (Or, you can still do it the other way, like "dbx = dropbox.Dropbox(...)" as long as you fill in credentials like above.)

I corrected but again error

import sys
import dropbox
from dropbox import DropboxOAuth2FlowNoRedirect
from dropbox.files import WriteMode
import time

while True:
    with dropbox.Dropbox(oauth2_access_token='sl access token',
                     oauth2_access_token_expiration=14400,
                     oauth2_refresh_token='refresh token',
                     app_key='app key',
                     app_secret='app secret') as dbx:
        try:
            with open('rtk.txt', 'rb') as f:
                file_contents = f.read()   
            dbx.files_upload(file_contents, '/rtk.txt', mode=dropbox.files.WriteMode('overwrite'))
        except Exception as e:
            print(f"An error occurred: {e}")
    time.sleep(60)

Showing error: "An error occurred: '>=' not supported between instances of 'datetime.datetime' and 'int'"

This error is indicating that oauth2_access_token_expiration requires a datetime, but you're now passing in an int. You should pass in a datetime for that. Or, you can just omit oauth2_access_token_expiration entirely and the SDK will just handle it as needed.

Remove this line? 

oauth2_access_token_expiration=14400,

Yes, either remove it or supply the correct type (datetime).

For now this code is perfectly working but I still want to open this topic 4 hours more to confirm if program doesn't die after that!

import sys
import dropbox
from dropbox import DropboxOAuth2FlowNoRedirect
from dropbox.files import WriteMode
import time

while True:
    with dropbox.Dropbox(oauth2_access_token='<access token>',
                     oauth2_refresh_token='<refresh token>',
                     app_key='<app key>',
                     app_secret='<app secret>') as dbx:
        try:
            with open('rtk.txt', 'rb') as f:
                file_contents = f.read()   
            dbx.files_upload(file_contents, '/rtk.txt', mode=dropbox.files.WriteMode('overwrite'))
        except Exception as e:
            print(f"An error occurred: {e}")
    time.sleep(60)