# API status codes
## Status codes
The API server responds contain a status code specifying the status of the response. The table below lists all the status codes and messages returned by the API server:
| Code | Message | Explanation |
| ---- | ----------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 20 | OK | The request was processed successfully. The response might also contain the **data** parameter containing data returned from the server. |
| 22 | Maintenance mode | The API servers have entered in maintenance mode and cannot complete any requests. In this case you should try again later. |
| 30 | Missing mandatory parameter | The request does not contain one or more required parameters. There are at least 3 required parameters for every request: **apiKey**, **signature** and **action**. Other methods may also have extra mandatory parameters. Please check the API Reference for more information. |
| 31 | Requests per second limit exceeded | There were too many requests per second made with the same API key. |
| 32 | Requests per minute limit exceeded | There were too many requests per minute made with the same API key. |
| 33 | Uploads per month exceeded | You have exceeded the maximum number of uploads allowed per month. |
| 34 | File size too large | The file you have uploaded has a size that exceeds the maximum file size allowed. For more information please see the [limitations](/api-limitations.md) imposed by the API. |
| 35 | Flipbook maximum pages number exceeded | You have uploaded a document that exceeds the maximum of 500 pages allowed. For more information please see the [limitations](/api-limitations.md) imposed by the API. |
| 36 | Multiple files upload not allowed | Flipsnack API allows only one file per upload request. Upload requests are made via the [collection.create](/api-reference/api-method-collection.create.md) method. |
| 37 | Delete flipbook not available for this flipbook | *deprecated* |
| 38 | Flipbook is in processing state | Publishing a flipbook may take a few seconds. You can check the **collectionStatus** at regular intervals (e.g., every few seconds) using the [collection.getCollection](/api-reference/api-method-collection.getcollection.md) method. Continue making requests to [collection.getCollection](/api-reference/api-method-collection.getcollection.md) until the **collectionStatus** has a value other than processing. |
| 40 | Bad request | - You made a POST request for an API call that is not uploading files.
- You made a GET request for an API call that uploads files.
- Your request is incorrectly formatted or the URL is invalid.
|
| 41 | Invalid credentials | The API key provided in the request is invalid. |
| 42 | Invalid action | The API method you specified in the request is incorrect. Please see the API Reference for the list of possible methods. |
| 43 | Forbidden | You are not allowed to access the specified flipbook: it has been deleted or the flipbook belongs to another user. |
| 44 | Invalid signature | The signature you provided is incorrect - it does not match the request. |
| 45 | Invalid file format | The file you are trying to upload has an incorrect file type. For more information please see the [limitations](/api-limitations.md) imposed by the API. |
| 46 | Invalid flipbook hash | You are trying to access a flipbook that does not exist. |
| 47 | Invalid flipbook hash | You are trying to access a flipbook that does not exist. |
| 50 | Operation failed | An error occurred on the server and the request could not be completed. In this case you should resend the request after a few seconds. If the request still fails after several attempts, please contact us. |
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