Recently, 5ch has been under attack by scripters and spammers. As a counter measure, (and because 5ch management is too retarded to put a CAPTCHA on this site) non-Japanese IPs can no longer post on any board on this site.
Which means boards made for foreigners such as dejima and the embassy ("8") boards have been now rendered useless.

If you wish to post, you can try using Tuxler with the residential VPN mode. You can also try SoftEther VPN Gate and try multiple Japanese IPs until you find one that isn't already banned.
If you wish to have a good experience on 5ch just like that of an ordinary 5ch user that lives in Japan, your only choice is to buy UPLIFT, though.
I don't think most people will want to give money to the terrible owners of this site though.