I followed this tutorial: Advanced Setup Only: Allowing SSL / HTTPS for your Discourse Docker setup
Could you try this command again? It returned the following for me:
Summary
$ openssl s_client -connect dungeon.gg:443
CONNECTED(00000005)
depth=0 OU = Domain Control Validated, OU = PositiveSSL, CN = dungeon.gg
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 OU = Domain Control Validated, OU = PositiveSSL, CN = dungeon.gg
verify error:num=21:unable to verify the first certificate
verify return:1
---
Certificate chain
0 s:/OU=Domain Control Validated/OU=PositiveSSL/CN=dungeon.gg
i:/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=COMODO RSA Domain Validation Secure Server CA
---
Server certificate
-----BEGIN CERTIFICATE-----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=
-----END CERTIFICATE-----
subject=/OU=Domain Control Validated/OU=PositiveSSL/CN=dungeon.gg
issuer=/C=GB/ST=Greater Manchester/L=Salford/O=COMODO CA Limited/CN=COMODO RSA Domain Validation Secure Server CA
---
No client certificate CA names sent
Server Temp Key: ECDH, P-384, 384 bits
---
SSL handshake has read 2666 bytes and written 358 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 4096 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES128-GCM-SHA256
Session-ID: 6038753C9F271BE81C5D22DFF4935E5AFECCE16C9FB6EECAEF5B6EE0D37F8908
Session-ID-ctx:
Master-Key: 93CE5931402313B65E0CD9C74A34CD52AF1B152DC03F364B6A8009D434C1A958FDFC6BB0D297608E47B3A3722AD21E4E
Start Time: 1546388599
Timeout : 7200 (sec)
Verify return code: 21 (unable to verify the first certificate)
---
closed