How does PKCE help prevent "error 401 invalid_client" in single-page applications (SPAs)?

PKCE (Proof Key for Code Exchange) doesn't directly prevent "error 401 invalid_client" *itself*. However, it mitigates the risk of authorization code interception, which can lead to the attacker using *their* (incorrect) client credentials, causing an error. PKCE primarily secures the authorization code grant flow in public clients (like SPAs) by binding the authorization code to the client that initiated the request, making it more difficult for an attacker to misuse a stolen authorization code, thus potentially reducing the opportunities for a client-related error further down the flow.