I don't think using login-by=https is the way to do it. Besides, you would need a SSL certificate installed.
The https protocol causes some strange problems with the hotspot walled garden. The hotspot uses dns cache to determine if the request should be allowed. The problem is some payment sites, like PayPal, use the dns as a form of load balancing, and the TTL on the resolution is very short, like a minute or less in some cases.
I use authorize.net, and they do not use dns as load balancing, so I use both the domain in "/ip hotspot walled-garden", and the ips in "/ip hotspot walled-garden ip".
So I will suggest the same approach for you. It appears that netcash does not use dns to load balance. Try this:
/ip hotspot walled-garden ip
add dst-address=184.108.40.206 action=accept
resolves to 220.127.116.11