When i select the Horizon Rally, game says: Horizon Rally expansion will be available to download since 18th December.
When i select the Buy Season Pass option, game displays Xbox Live Marketplace without Buy option. (only with Cancel option)
What happened with the FH DLC?
Because on October 20th, 2016, Forza Horizon reached “End of Life” Status which means that it won’t be supported anymore. Since that date, DLC has been removed from store, which means you can no longer buy the DLC.