# API error handling Source: https://developer.avalara.com/tax-docs-en/errors/api_error_handling/ # API error handling When a TaxDocs API call produces an error, it responds using the standard [HTTP error response codes](https://en.wikipedia.org/wiki/List_of_HTTP_status_codes "https://en.wikipedia.org/wiki/List_of_HTTP_status_codes"). Response codes between 400 and 499 are called **Client Errors**, and indicate a mistake in an API call. Response codes between 500 and 599 refer to internal errors within TaxDocs Monitor itself.  **HTTP Code** **Description** **Observation** 400 Bad Request subscriptionId is empty Subscription ID was not informed in the token or in the subscriptionId parameter 400 Bad Request startIssueDate is empty StartIssueDate parameter was not informed 400 Bad Request endIssueDate is empty Parameter endIssueDate was not informed 400 Bad Request startIssueDate greater than endIssueDate A date was entered in the startIssueDate parameter after the informed date in the parameter endIssueDate 400 Bad Request Select an interval less than or equal to issueDateMaxRange days startIssueDate and endIssueDate specify a time range greater than issueDateMaxRange days 400 Bad Request $top parameter must be between 0 and 1000 Invalid $top parameter (missing or out of the allowed range) 400 Bad Request $top and $count can not be equal 0 and false simultaneously Invalid $top and $count parameters (cannot be equal to 0 and false simultaneously) 400 Bad Request $skip parameter must be equal to or greater than 0 Parameter $skip is invalid (absent) 400 Bad Request Invalid OData Parameters. MessageId: 00000000-0000-0000-0000-000000000000 A syntax error occurred when using any of the following parameters: $top, $skip, $filter, $orderby, $count, $select 400 Bad Request - The server could not understand the request due to invalid syntax 401 Unauthorized A valid token was not provided for authentication 403 Forbidden A non-app token was informed for the authentication 403 The request was denied because you do not have permission to make this alteration 404 The URL requested is invalid or the resource requested does not exist 429 The user has sent too many requests in a given amount of time (“rate limiting”) 500 Internal Server Error Unexpected error while listing invoices. MessageId: 00000000-0000-0000-0000-000000000000 An unexpected error occurred in the operation 500 The server has encountered a situation it doesn't know how to handle 503 The server is not ready to handle the request [Previous](/tax-docs-en/authentication/certification_requirements) [Next](/tax-docs-en/concepts/fiscal_document)