HI Kumar,
What I see is your gateway application end point url uses HTTPS via port 443, are you handling the certificate properly in the netweaver gateway, you have to reach to the BASIS team or the one who has configured gateway ? Also can you see wheather HTTPS has port has been configured at 443
Can you check whether you are able to fetch the metadata by http ?
Are you able to download the file by appending $metada to the application end point?
Regards,
Srinivas Divakarla