have you preformed a reset on iptv66 site? if yes then your issue might be related to maintenance. I would wait because some had issue and after few hours they reported back that its working fine for them now.
buffering depends on many things, your server, your device, your setup, your network, your isp.....etc.
here in Africa my speed is 5-7 Mbps and 98% I get good tv. so 30-40 Mbps with vpn still a lot. :)
did you type correct url? did you attach your Mac address correctly? did you perform a reset at provider site after you attach Mac address?
are you using 66, rocket, nfps?