Invalid grant_type issue

While Constructing the OAuth2 Request I got a error for invalid grant_type

what is your grant_type?

grant_type=authorization_code  for OAuth2 Step 5

grant_type=refresh_token   for OAuth2 Step 6

Make sure no typo, extra space, character, line etc. I have some curl command problems last time. It gave me errors even I think I sent the correct curl command line. If you think the constructing OAuth2 request is correct, try the different computer and network to see if it makes any difference.