'Token has been expired or revoked' - Google OAuth2 Refresh token gets expired in a few days

I am using Google Analytics API to fetch analytics data. I tried to authenticate it using following steps:

Created OAuth client ID in https://console.developers.google.com/ credentials section.
In consent screen I had set publishing status as testing
In OAuth 2.0 Playground I got the refresh token using above generated client id and client secret
Then I am using it to generate access token through it.

But after a few days, the refresh token expires although it is mentioned that the refresh token's validity is life long.

Solution

If your app is in testing mode then user tokens will expire in 7 days. Please find this explanations here: https://support.google.com/cloud/answer/10311615#zippy=%2Ctesting