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Error codeError MessageDescriptionExamples

API blocked

This API has been blocked temporarily. Please try again later or contact the system administrators.

Invoke an API which is in the BLOCKED lifecycle state
Message throttled out

The maximum number of requests that can be made to the API within a designated time period is reached and the API is throttled for the user.

Invoke an API exceeding the tier limit 
Hard limit exceededHard throttle limit reachedInvoke an API exceeding the hard throttle limit
900802Resource level throttle outMessage is throttled out because resource level has exceededSending/Receiving messages beyond authorized resource level
900803Application level throttle outMessage is throttled out because application level is exceededSending/Receiving messages beyond authorized application level

Unclassified authentication failure

An unspecified error has occurredBackend service for key validation is not accessible when trying to invoke an API

Invalid credentials

Invalid authentication information providedUsing an older access token after an access token has been renewed.

Missing credentials

No authentication information providedAccessing an API without the Authorization: Bearer header

Incorrect access token type is provided

The access token type used is not supported when invoking the API. The supported access token types are application and user accesses tokens. See Access Tokens.

Invoke API with application token, where the resource only allows application user tokens

No matching resource found in the API for the given request

A resource with the name in the request can not be found in the API.Invoke an API resource that is not available

The requested API is temporarily blocked

Happens when the API user is blocked.Invoke API resource with a subscription that has been blocked by the API publisher

Resource forbidden

The user invoking the API has not been granted access to the required resource.Invoke an unsubscribed API

The subscription to the API is inactive

The status of the API has changed to an inaccessible/unavailable state.Invoke an API resource with a subscription that has not yet been approved by the administrator.

The access token does not allow you to access the requested resource

Can not access the required resource with the provided access token. Check the valid resources that can be accessed with this token.

Invoke API resource with an access token that is not generated to be used with the resource's scope.
102511Incomplete payloadThe payload sent with the request is too large and the client is unable to keep the connection alive until the payload is completely transferred to the API GatewaySending a large PDF file with the POST request



The HTTP Status Codes and the corresponding error codes from the error responses are given below.

HTTP Status CodeError Code
401900901, 900902, 900905, 900907, 900909
403900906, 900908, 900910
429900800, 900802, 900803
503700700, 900801

Transport error codes

Error CodeDetail
101000Receiver input/output error sending
101001Receiver input/output error receiving
101500Sender input/output error sending
101501Sender input/output error receiving
101503Connection failed
101504Connection timed out (no input was detected on this connection over the maximum period of inactivity)
101505Connection closed
101506NHTTP protocol violation

Connection canceled

101508Request to establish new connection timed out
101509Send abort
101510Response processing failed

If the HTTP PassThrough transport is used, and a connection-level error occurs, the error code is calculated using the following equation:

Error code = Base error code + Protocol State

There is a machine state in the transport sender side, where the protocol state changes according to the phase of the message.

Following are the possible protocol states and the description for each:

Protocol State
Protocol State
REQUEST_READY (0)Connection is at the initial stage ready to send a request
REQUEST_HEAD(1)Sending the request headers through the connection
REQUEST_BODY(2)Sending the request body
REQUEST_DONE(3)Request is completely sent
RESPONSE_HEAD(4)The connection is reading the response headers
RESPONSE_BODY(5)The connection is reading the response body
RESPONSE_DONE(6)The response is completed
CLOSING(7)The connection is closing
CLOSED(8)The connection is closed

Since there are several possible protocol states in which a request can time out, you can calculate the error code accordingly using the values in the table above. For example, in a scenario where you send a request and the request is completely sent to the backend, but a timeout happens before the response headers are received, the error code is calculated as follows:

In this scenario, the base error code is CONNECTION_TIMEOUT(101504) and the protocol state is REQUEST_DONE(3).


Error code = 101504 + 3 = 101507

These Transport error codes are used in Advanced Configurations of Endpoints.

Custom error messages

To send a custom message with a custom HTTP status code, you execute an additional sequence that can generate a new error message. You then override the message body, HTTP status code and other values.


WSO2 API Manager has the following default fault sequences located in <APIM_HOME> /repository/deployment/server/synapse-configs/default/sequences directory.

Fault SequenceDescription

This is the primary fault sequence that gets invoked when an error occurs during the execution of an API resources

main.xmlThis sequence is called when the endpoint being called does not exist
auth_failure_handler.xmlThis sequence is called when an API authentication error is encountered
production_key_error.xmlThis sequence is called when a Production key is used to invoke an API that does not have a Production endpoint defined
sandbox_key_error.xmlThis sequence is called when a Sandbox key is used to invoke an API that does not have a Sandbox endpoint defined
throttle_out_handler.xmlThis sequence is called when a given request to an API gets throttled out
token_fault.xmlThis sequence is called when there is an error in invoking the token API
resource_mismatch_handler.xmlThis sequence is called when a matching resource cannot be found by the gateway to the corresponding resource being invoked

The default sequences can also be customized as shown in the section above.