Try this, I had to AI as i've never seen that error…
1. What Causes It
Unclosed Auth Window: An existing OAuth popup window opened during a previous "Add Account" attempt was minimized, moved behind other windows, or got stuck loading, so Chrome considers the auth flow active.
Rapid Multi-Clicking: Clicking "Add Account" multiple times rapidly triggers two concurrent chrome.identity.launchWebAuthFlow() API calls.
Stale Callback State: The previous flow completed on Google's end, but the extension's redirect URL listener didn't catch the callback or close the flow gracefully.
2. Immediate User Fixes
Check for Hidden Popups: Look at the OS taskbar/dock or press Alt + Tab (Cmd + Tab on Mac) to see if a sign-in window is open in the background, then complete or close it.
Restart the Browser: Fully closing and reopening Chrome terminates all stuck launchWebAuthFlow instances.
Re-open Extension Popup/Options: Closing and reopening the extension options tab resets the local UI state before trying again.
