HTTP Status Codes - Stellar Developer Docs

Stellar uses conventional HTTP response codes to indicate the success or failure of an API request. In general:

Codes in the 2xx range indicate success.
Codes in the 4xx range indicate an error that failed given the information provided
Codes in the 5xx range indicate an error with the Horizon server.

There are two types of Status Codes:

HTTP Status Code Types
Standard Status Codes	Generic HTTP responses.
Horizon-Specific Status Codes	Errors that are unique to Horizon.