403 403 Forbidden

The server understood the request but refuses to authorize it.

When you'll see it

When the server knows what you ask for but refuses: your account lacks permission, your IP or country is blocked, or a firewall stopped the request.

The difference from 401: logging in again won't help if the account simply lacks permission.
Your CDN or WAF logs, since a security rule often sends the 403, not your application.
File permissions and directory listing settings on the server.
For SEO, that crawlers aren't blocked: a page that keeps returning 403 can drop out of the index.

HTTP/1.1 403 Forbidden
Content-Type: application/json

{"error": "this token can't delete projects"}

Google treats 403 like 404 over time. If a page consistently returns 403, it will be dropped from the index.