# App token lifecycle management
In this document, we are going to understand the whereabouts of the App token Generation and its lifecycle management.
App token is used to authenticate the API requests coming from the client side. It can be easily generated using the App Token generation [API](https://isac.happay.in/v2/docs#authentication). Once this has been generated it needs to be passed in the HTTP headers of all the API requests being made.
The App token stays valid for 25 Hours from its generation and post this time frame we need to regenerate it for security purposes.
In case the APP token has expired or is not right then you get the below message in the API response.
**401 unauthorized:**
Hence it is suggested to regenerate the APP token in case this error is encountered while making the API calls.
we request you to build a logic where in case the 401 error occurs during any operation the app token is generated directly during the same process, and then the further transaction can proceed further once the app token has been updated without interrupting the user operation sequence.
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