How do I resolve "The underlying connection was closed: An unexpected error occurred on a send." in Sage PRO?
Restart your Sage server
Ensure you are using the current SHA 256 certificate
If you are still on SHA 1 certificate you need to use a special service URL that supports SHA1.
NOTE: We are planning to discontinue the use of SHA1 certificate on May 10, 2017 (Avalara AvaTax SHA1 Certificate Change May 2017). In the meantime, we've created a special service URL that still supports SHA1.