My solution was to use a VPN to download, seems like an issue with my internet service provider.

Hello, Trying to download PREPAR3D® V5.2 ACADEMIC, I get an error: The connection for this site is not securecloud.prepar3d.com sent an invalid response. Try running Windows Network Diagnostics. ERR_SSL_PROTOCOL_ERROR I've tried different machines and Firefox and Edge Please help! Thank you, DF06