Mirage Isle Gilda Star shops work now.
Buying from the Gilda Star stands did nothing before: you clicked Confirm and nothing happened. That is fixed. Click Confirm and the design goes straight into your bag and the Gilda Stars come out.
This covers every Gilda Star stand in the game (148 of them), including the house designs (Thatched Farmhouse, Rustic and Tudor Rose Cottage), the Aquafarm, and the Harpoon and Adventurer's Clipper ship designs.
Nobody was charged for any of the clicks that failed before the fix.
To buy: have the full Gilda Star price in your bag and stand at the stand.
Thanks to 크미 (Kmi) for the report.