Do I always have to keep up with the latest version of the API?
It’s not required that you keep up with the latest version of the API however it is recommended that you do update the version on some cadence. In most cases, migrating to a new Square-Version should be straightforward, with known differences listed in the related changelog.
To test migrations, developers can override the default Square-Version of an application by explicitly setting the preferred Square-Version in the HTTP header of REST calls to the Square API. Requesting an API version that does not exist returns an error. Successful API responses include the Square-Version header to indicate the API version used to process request. 