Please see the below image. The status code is 200 but I don't see any refresh token.
That isn't the correct URL for requesting the refresh/access tokens using your authorization code; it looks like that's the URL a user is sent to after initiating the OAuth connection:
In order to obtain the authorization code, a user needs to navigate to your authorization URL and then select their portal. Once they've approved the app, they'll be redirected to you
redirect_url with an authorization code appended to the URL. Once you have that authorization code, you can make the following request to get the refresh/access tokens: