Updated Google Refresh Token Expired troubleshooting section

docs/EN/SettingUpAaps/BrowserBuild.md

@@ -325,6 +325,15 @@ Variants ending with “Debug” indicates that the APK will be built in debug m
 
   ![aaps_ci_html_not_found](../images/Building-the-App/CI/aaps_ci_html_not_found.png)
 
+(aaps-ci-google-token-expired)=
+### Google Refresh Token Expired
+  - Google OAuth2 refresh tokens will expire if not used for 6 months, and may also become invalid under other conditions (e.g., you have changed your Google account password, or manually revoked access). For more details, see the [Google OAuth2 documentation](https://developers.google.com/identity/protocols/oauth2).
+  - You will see an error indicating that the access token is invalid, as shown below:
+
+  ![aaps_ci_token_expired](../images/Building-the-App/CI/aaps_ci_token_expired.jpg)
+
+  - If your build fails due to an expired or revoked Google refresh token, you will need to redo the [Google Drive Auth](#aaps-ci-google-drive-auth) steps to obtain a new `GDRIVE_OAUTH2` token and update the secret in your GitHub repository, then re-run the build workflow.
+
 (aaps-ci-disable-software)=
 ### Disable Software That May Interfere With OAUTH Verification
   - Disable any VPN or security app (firewall, antimalware,...) on the phone before trying to get the OAUTH key.