SSL certificate error in Mongo

This is what I did exactly to establish an SSL connection.

1 Use openssl to generate client and server key (c.pem, s.pem)

2 Use openssl to generate client key request and server key request

3 Get a CA to sign both reqs and get certificates: c.cer, s.cer

4 concatenate c.pem and c.cer and get client.pem, similarly get server.pem

Now start the server:

mongod --sslMode requireSSL --sslPEMKeyFile server.pem -sslCAFile caroot.cer

start the client:

mongo --ssl --sslCAFile caroot.cer --sslPEMKeyFile client.pem

And now I am getting the error:

E NETWORK SSL peer certificate validation failed:certificate not trusted

Any thoughts on why this isn't working?