I received an error code from the DataCite API, what does it mean?

4xx Client Error

400 Bad Request - Check the docs again and try to reproduce.
401 Unauthorized - Check your password.
403 Forbidden - Check your password or validate that you are updating a DOI/prefix/repository you have permissions for.
404 Not Found - The resource is not found, be it fetching a DOI/Repository/Member details.
405 Method Not Allowed - The http method on the request made is not supported. Check documentation.
422 Unprocessable Entity - Check the contents of your request, the system understood but it was unable to process it. For a DOI update this might be invalid URL or metadata is invalid.

5xx Server Error

500 Internal Server Error - Try to reproduce and report steps that caused it.
502 Bad Gateway - Most likely a temporary issue, try again.
503 Service Unavailable - Check our status page status.datacite.org.
504 Gateway Timeout - Check our status page/releases status.datacite.org.

Error code	Message	Possible Solution
400		Bad Request - Check the docs again and try to reproduce.
401	Bad credentials.	Unauthorized - Check your password.
403	You are not authorized to access this resource.	Forbidden - Check your password or validate that you are updating a DOI/prefix/repository you have permissions for.
404	The resource you are looking for doesn't exist.	Not Found - The resource is not found e.g. it fetching a DOI/Repository/Member details.
405		Method Not Allowed - The http method on the request made is not supported. Check documentation.
422		Unprocessable Entity - Check the contents of your request, the system understood but it was unable to process it. For a DOI update this might be invalid URL or metadata is invalid.
500		Internal Server Error - Try to reproduce and report steps that caused it.
502		Bad Gateway - Most likely a temporary issue, try again
503		Service Unavailable - Check our status page status.datacite.org.
504		Gateway Timeout - Check our status page/releases status.datacite.org.