Hi Ankit,
Thank you for reaching support. An access token has an expiration time (based on the expires_in value) after which the token is no longer valid. You can use the refresh token to refresh an expired access token. Please refer to this guide to create OAuth2 refresh token to automatically renew OAuth2 access. By default, our client libraries automatically refresh expired access tokens. Let us know if this helps
Regards,
Nikisha Patel, Google Ads API Team