@nrajesh - Yes, you are right ..refresh token is used to update the access token. We need hit a separate call to update the refresh token.
whenever we refresh the accessToken, the response having accessToken and refreshToken also. but i have stored accessToken only in my DB for further actions, not refresToken. Confirm we dont need to store refresToken ? whatever we got at initial stage that is for lifetime correct.
@nrajesh - Yes, you do not need to store the refresh token, if you already have it. It will not be expired until it is blacklisted or refreshed using rest API call.
Here is an article for refresh token which will give you more info regarding the refresh token.