Installed Self-Signed Cert: Unable to Parse TLS Packet Header

[Tally]

I'm running connecting to Transmission in a LAN network (technically by VPN) and it works excellently with an insecure connection but attempting a secure connection fails and produces the following error after installing the server's intermediate or chain certificate under the checked "Server uses self-signed certificate" box. I have successfully installed this certificate onto several computers and the Android system, so I believe the certificate itself is not the issue.

The server is Caddy 2.6.2.

Error: org.equeim.tremotesf.rpc.RpcRequestError$NetworkError: Network error when performing HTTP request

Caused by: javax.net.ssl.SSLException: Unable to parse TLS packet header

I have a suspicion this is user error, and, if so, I apologize but I couldn't locate a more apt place to seek clarification. Thanks.