You clearly haven't played the game, and there is no feature being hidden. Discord is not required.
"Join discord for additional rewards". Even my screenshot shows that my friend. This was not mentioned within the mods description.
A lot of people complain about this private server because of that. Thats it. If you only have access to certain advertised features trough third party such as discord thats simply not allowed here.
Also as an addition. If certain things only work a certain way and that way is nowhere descriped within the features description, it counts as "not working" and thats it.
So if a feature such as "daily diamonds" as an example is mentioned but nowhere is written HOW to get those without scrolling trough 20 pages of comments, it counts as Not Working. Simple as that.
And according to how many people complained and reported this thread, the issue seems to be really real.
Last but not least
Do I have to say more? I don't think so.