The api-version request header specifies the version of the API platform that should process the request. Sending this header with each API request ensures that your integration will continue to work in the way it was designed, and will not be negatively affected by future upgrades that could potentially break it.
You can find the recent changes in our API here - ChangeLog
To ensure that your request uses the correct API version, make sure to include the api-version header in all API requests. If the api-version header is not included in an API request, then 1.0.0 is used as the default API version.
API version 1.0.0 will no longer be available, effective November 1, 2019. As of this date, any integrations still using 1.0.0 resources will not work. You should update your integration to use version 1.3.0 resources as soon as possible.