Hi,
The problem happens when watcher attempts to download the file from https://xyz as it cannot validate the TLS certificate that is presented for https://xyz
I am assuming the URL is pointing to your Kibana instance. What are your SSL settings in Kibana? Are you using a self signed certificate for TLS in Kibana ? ( Step 1 in this https://www.elastic.co/guide/en/kibana/6.3/configuring-tls.html#configuring-tls )