I deleted the account that logged in through Google; the error is shown in the screenshot. According to the solutions from other posts, there might be a "hidden identity" that has not been completely deleted. Then I tried to use Server SDK to list all identities. But it showed {"identities": [], "total": 0}. How to deal with this?
TL;DR
Title: Issue with OAuth Google: 400 bad request
Developer encountered error after deleting Google-linked account. Attempted solution did not work.
Solution: In this case, developers can try revoking access and re-authorizing with Google to resolve the issue.