App registration is required if you want other Daylite users to authorize access to their accounts through your application.

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Important:
Localhost redirect URLs and homepage URLs are not allowed. All redirect URLs must point to a dedicated, publicly accessible endpoint configured specifically for API integration.
Before applying, consider whether a personal token will meet your needs. OAuth apps and personal tokens operate the same way in terms of access and token expiration, both require refreshing the token every hour.
The key difference: OAuth apps are intended for developers who want other Daylite users to authorize access through their registered app. If you're only accessing the API for your own account, a personal token is likely more appropriate.