> ## Documentation Index > Fetch the complete documentation index at: https://resend.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Errors > Troubleshoot problems with this comprehensive breakdown of all error codes. ## Error schema Resend uses standard HTTP response codes for success and failure notifications, and errors are further classified by type. ### `invalid_idempotency_key` * **Status:** 400 * **Message:** Idempotency keys, if present, must have between 1 and 256 characters. * **Suggested action:** Retry with a valid idempotency key. ### `validation_error` * **Status:** 400 * **Message:** An error was found with one or more fields in the request. * **Suggested action:** The message will contain more details about what field and error were found. ### `missing_api_key` * **Status:** 401 * **Message:** Missing API key in the authorization header. * **Suggested action:** Include the following header in the request: `Authorization: Bearer YOUR_API_KEY`. ### `restricted_api_key` * **Status:** 401 * **Message:** This API key is restricted to only send emails. * **Suggested action:** Make sure the API key has `Full access` to perform actions other than sending emails. ### `email_above_quota` * **Status:** 403 * **Message:** You can't retrieve this email's content because it was above quota when received. * **Suggested action:** [Upgrade your plan](https://resend.com/settings/billing) to increase your quota. ### `invalid_permission` * **Status:** 403 * **Message:** Access token is missing required scopes. * **Suggested action:** Request an access token that includes the scopes required by this endpoint. ### `restricted_api_key` * **Status:** 403 * **Message:** API key is not active * **Suggested action:** Check the API key on the [API Keys page](https://resend.com/api-keys) and create a new one if needed. ### `suspended_api_key` * **Status:** 403 * **Message:** This API key is suspended * **Suggested action:** [Contact support](https://resend.com/contact) if you believe this is a mistake. ### `validation_error` * **Status:** 403 * **Message:** You can only send testing emails to your own email address (`youremail@domain.com`). To send emails to other recipients, please verify a domain at resend.com/domains, and change the `from` address to an email using this domain. * **Suggested action:** In [Resend's Domain page](https://resend.com/domains), add and verify a domain for which you have DNS access. This allows you to send emails to addresses beyond your own. [Learn more about resolving this error](/docs/knowledge-base/403-error-resend-dev-domain). ### `validation_error` * **Status:** 403 * **Message:** The `domain.com` domain is not verified. Please, add and verify your domain. * **Suggested action:** Make sure the domain in your API request's `from` field matches a domain you've verified in Resend. Update your API request to use your verified domain, or add and verify the domain you're trying to use. [Learn more about resolving this error](/docs/knowledge-base/403-error-domain-mismatch). ### `validation_error` * **Status:** 403 * **Message:** The `example.com` domain has been registered already. * **Suggested action:** Verify you are signed in to the correct Resend account and check whether a teammate already added the domain. If you still cannot access it, [contact support](https://resend.com/help). [Learn more about resolving this error](/docs/knowledge-base/domain-already-registered). ### `not_found` * **Status:** 404 * **Message:** The requested endpoint does not exist. * **Suggested action:** Change your request URL to match a valid API endpoint. ### `method_not_allowed` * **Status:** 405 * **Message:** Method is not allowed for the requested path. * **Suggested action:** Change your API endpoint to use a valid method. ### `concurrent_idempotent_requests` * **Status:** 409 * **Message:** There is another request in progress with the same idempotency key. * **Suggested action:** Try the request again later. ### `invalid_idempotent_request` * **Status:** 409 * **Message:** This idempotency key has been used with this HTTP method and endpoint within the last 24 hours, but the request body was modified and doesn't match the original request. * **Suggested action:** Change your idempotency key or payload. ### `resource_locked` * **Status:** 409 * **Message:** Another request is already updating this resource. * **Suggested action:** Retry the request after a short delay. ### `invalid_attachment` * **Status:** 422 * **Message:** Attachment must have either a `content` or `path`. * **Suggested action:** Attachments must either have a `content` (strings, Buffer, or Stream contents) or `path` to a remote resource (better for larger attachments). ### `invalid_parameter` * **Status:** 422 * **Message:** The `parameter` must be a valid UUID. * **Suggested action:** Check the value and make sure it's valid. ### `missing_required_field` * **Status:** 422 * **Message:** The request body is missing one or more required fields. * **Suggested action:** Check the error message to see the list of missing fields. ### `missing_required_parameter` * **Status:** 422 * **Message:** The request is missing one or more required parameters. * **Suggested action:** Check the error message to see the list of missing parameters. ### `daily_quota_exceeded` * **Status:** 429 * **Message:** You have exceeded your daily email sending quota. * **Suggested action:** [Upgrade your plan](https://resend.com/settings/billing) to remove the daily quota limit or wait until 24 hours have passed. Both sent and received emails count towards this quota. ### `monthly_quota_exceeded` * **Status:** 429 * **Message:** You have exceeded your monthly email sending quota. * **Suggested action:** [Upgrade your plan](https://resend.com/settings/billing) to increase the monthly email quota. Both sent and received emails count towards this quota. ### `rate_limit_exceeded` * **Status:** 429 * **Message:** Too many requests. Please limit the number of requests per second. Or [contact support](https://resend.com/contact) to increase rate limit. * **Suggested action:** Read the [response headers](/docs/api-reference/introduction#rate-limit) and reduce the rate at which you request the API. This can be done by introducing a queue mechanism or reducing the number of concurrent requests per second. If you have specific requirements, [contact support](https://resend.com/contact) to request a rate increase. ### `application_error` * **Status:** 500 * **Message:** An unexpected error occurred. * **Suggested action:** Try the request again later. If the error does not resolve, check our [status page](https://resend-status.com) for service updates. ### `service_unavailable` * **Status:** 503 * **Message:** API is temporarily unavailable * **Suggested action:** Try the request again later. Check our [status page](https://resend-status.com) for service updates.