MQTT Connection using Certs (CA, Client, etc.)

Does anyone ever used MQTT connection using certificates (CA, Client, key file etc.).

We were using Basic Auth for MQTT so far, it was working fine. but now are moving to Certificates. I tried different combination but non of them worked.

1. Gave Certificates in MQTT SSL Properties Window
   1.  CA (Company RootCA Certificate) with .crt
   2. Client Certificate (tried with .pfx/.jks)
   3. KeyFile(.key) with pass
2. Tried giving Key File and Client Cert in ReadyAPI-> Preferences-> Security->SSL->KeyStore

Getting "Error during message publishing: org.eclipse.paho.client.mqttv3.MqttSecurityException "Bad user name or password", some times  "javax.net.ssl.SSLHandshakeException
"Received fatal alert: bad_certificate".

I'm Using ReadyAPI 3.51.0

Any help appreciated, TIA.