This achievement is very glitchy. As of right now, it may or may not unlock if you had already purchased the house prior to Update #23. It also won't unlock at all for some people, even if they hadn't purchased the house prior to Update #23. We have notified Playground Games of the issue. They haven't yet commented about it, but in the past they've had a good history of patching broken achievements in Forza Horizon 4.Update, June 23: An update was released this morning and people are now reporting that the achievement will unlock if you already owned the house prior to the update. If the achievent isn't immediately unlocking, you might have to set the house as your home or sit in the house for 5-10 minutes before it unlocks, but the achievement seems to be fixed.
The Sunflower Meadows house is near Ambleside and can be purchased for 200,000 credits. It becomes available to purchase after you qualify for the Autumn festival for the first time and are given The Gables
house for free.
Drive to the location shown in the image below and purchase the house, and the achievement will unlock.https://imgur.com/gallery/kx4HYSE
If you have never driven past the house before and don't have the treasure map enabled, the house won't show up on the map until you arrive. Don't worry, once you get there you will be able to purchase the house.
Purchasing the house will also unlock Horizon Promo which is required for these two achievements:
Unfortunately, if you already had the house purchased before Update #23, this achievement might not unlock. I already tweeted at Playground Games about the issue. Right now all we can do is let them know and hope for a patch. Playground Games have been doing a pretty good job at fixing some of the other broken achievements in Forza Horizon 4, so I'd expect they'll fix this one as well. If not, I have an idea of a workaround method that involves deleting your save and playing offline. I'll write it up and post it if we don't get a patch (or notice of a patch) within the next week.