If you have licensed Demand Forecasting but the Number of Licensed Demand Forecasting users shown in the Info button in Demand Forecasting parameters screen shows as "None" rather than a numerical value such as 3, 10, Unlimited etc.
Then check the Customer name on the D365 Client menu in the "?">About>Legal tab.
And check/ensure the spelling of the customer name matches 100% with the spelling of the customer name in the License file Farsight has supplied - including all upper and lower case letters. If there is any differences in the customer name between the license file Farsight have supplied and the D365FO environment, the Demand Forecasting licensed user cannot be determined.
You need to resolve this issue within D365 if possible. If you cannot resolve it we can issue an updated license file to match the changed customer name spelling.
But note: it is important that all D365 environments spell the customer name exactly the same as the installed Demand Forecasting license file.