When backwards-incompatible changes are made to the API, a new dated version is released. You can view your version and upgrade to the latest version in your dashboard settings.
We highly recommend upgrading to the latest API version. Upgrading allows you to keep up to date the with the latest features, bug fixes, and performance improvements.
To test a newer version of the API, you need to specify a version, in the HTTP header as shown in the documentation. The API will return an error if a version older than your current one is passed in.
See the API changelog for a full list of breaking changes.