From Authorize.NET:
The new PCI DSS requirements state that all payment systems must disable early TLS by 2018. Transport Layer Security (TLS), is a technology used to encrypt sensitive information sent via the Internet. TLS is the replacement for Secure Sockets Layer (SSL).
In preparation for this requirement, Authorize.Net plans to disable TLS 1.0 and TLS 1.1 on the following dates:
Sandbox: Already disabled
Production: September 18, 2017
iPayment 2017.04 and higher works with this change. Any versions older than 2017.04 will not work in the sandbox right now and in September they will stop working in production.
Please upgrade to iPayment 2017.04 or higher before September 18, 2017 to avoid downtime.