Some people have been having issues with loading the Root CA or certificate chain into the trusted store for CentOS.
RandyT with assistance from markljenkins was able to resolve this.
RandyT used certbot to obtain his SSL certificates from Let's Encrypt. He was able to get the certificate chain installed to the CentOS trusted store using the following:
chain.pem, which are the root and intermediate certs for Let's Encrypt into
/etc/pki/tls/certs and then running
You may need to restart zend.
To verify that the certificate chain has been installed correctly run
zen-cli getnetworkinfo and you should see
"tls_cert_verified": true, if the certificates have been installed correctly.