I suspect this is nothing to do with an internet connection. The Op thinks V23 is a Sony product which it is not. This error often is associated with an invalid e-mail or serial number. Was V23 key purchased from Magix?
@Casey-Cipoletti Try do a system restart, then temporarily disable all internet firewall and security protocol, then try and activate with the exact email and activation code you received from Magix.
@Steve_Rhoden why should @Casey-Cipoletti register Sony Vegas Pro 23 at Magix (and not at Sony)? When you got a Toyota, do you go to Mercedes-Benz for garantee/service...?
@Steve_Rhoden It's bizarre that more than 10 years after the latest release of a Sony Vegas Pro version ( version 13 in 2014), that new users to this forum are still able to get/purchase a recent Sony Vegas Pro ....!