For apps and integrations created through the Keka App Portal , developers need to follow a 3 step process:

First you need to read the OAuth token sent as as a query parameter ?code= to their Redirect URL as mentioned in the Keka App Developer Portal

Generate a access_token (24 hour validity) and refresh_token using the the Generate Access token using OAuth code endpoint
You can store the refresh_token in your system and use it to generate the access_token again using the Refresh token: Generate Access token using refresh token endpoint

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If you are looking for API Key based integration, please use the Generate Access Token using API Key endpoint