SSLError with Kong Mtls and CA Cert

Hi,
We are working with Kong-enterprise (DB enabled mode) and trying to integrate the Mtls plugin with one of the kong services. we have successfully stored the CA certificate using kong admin API (/ca_certificates).

We got the following error when we tried to invoke the service with a valid CA certificate:
http: error: SSLError: HTTPSConnectionPool: Max Retries exceeded with URL:

Do we need to do any additional configuration?

Thanks in advance!!