Basically just bought it on Amazon through here: https://www.amazon.com/Forza-Horizon-3-Ultimate-Xbox-One/dp/B01GW3LRD2?th=1 (change ultimate to standard). Make sure it's the digital version.

Bought with European VISA, received a code, redeemed it on Belgian Microsoft Store.

Horizon 3 is available for $39 - https://www.amazon.com/Forza-Horizon-3-Xbox-One/dp/B01GW3LRD2/