> For the complete documentation index, see [llms.txt](https://docs.tryterra.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tryterra.co/help-center/help-topics/no-data/webhooks-background-delivery-stopping/upgrade-api-version-for-delivery.md).

# What's the recommended delivery method?

Delivery instability is generally not specific to a destination like [Firebase](https://docs.tryterra.co/health-and-fitness-api/integration-setup/setting-up-data-destinations/firestore).

* If you're on an older API version, **upgrading to the latest** improves event delivery speed, error handling, retries and consistency. The upgrade is handled Terra-side with no code changes and is backwards compatible.
* After a successful connection, you may also need a [historical data request](https://docs.tryterra.co/health-and-fitness-api/managing-user-health-data/requesting-historical-data) to retrieve existing historical data.