4xx Client errors
405 Method Not Allowed
The address exists but doesn't accept this request method.
Common causes
- Sending POST to an endpoint that only takes GET, or similar.
How to fix it
- Use the method the API documents; the Allow header lists the accepted ones.
Find out the moment your site returns 405
Spot Downtime monitors count this as down and alert you, since visitors see an error. (The public “Is it down?” checker treats 4xx answers from big sites as online, because many refuse automated requests.)