We have updated the way we manage our network infrastructure to be more responsive to events and business need. In order to support these changes, we changed the IP addresses used by our API endpoints.
We will be testing removal of old IP Addresses on 04/03/2019 between 9:00am to 11:00am PT, during this time no connections will be allowed on the old IP Addresses. We will then completely remove these old IP Addresses over the next month.
For more details, see our support article, Authorize.Net Domains and IP Addresses:https://support.authorize.net/s/article/Authorize-Net-Domains-and-IP-Addresses