Thanks for your feedback.
There are no regional, national or IP address restrictions to that url or the domain name altairsound.com
The IP address is 184.108.40.206 which is a shared server srv215-218.hosting24.com
I think the problem could be Twitter’s Domain Name Servers (DNS) not having correct data to translate the domain name into the IP address. This would explain why so many people have the same problem. This can happen when the Routing Table on the DNS is not refreshed properly, so that address information does not promulgate properly.
It would also explain why it happened so suddenly, in May, after working well for some time.
Twitter’s DNS have old data, that appears to be the problem. You need to refresh the routing tables on your servers, I believe.
It’s definitely the DNS!!