You should try emailing them through whichever way you bought the menu.
For example I bought this menu through Shoppy with PayPal.
When my key didn’t work immediately I emailed the customer service department there.
Granted they never got back to me but my menu keys were working the next morning.
I have never been able to get on their discord either.
It’s probably that someone just needs to process the transaction in their end as in activate your key.
I’m sure they will probably get around to it soon.