When I try to generate a Gen 9 Vivillon with an Archipelago Pattern, I get the error message "Invalid: Unable to match an encounter from the origin game." The met location is one where Vivillon spawn, and the met level matches the level of the spawns. The only reason I can think of for why it returns an error message is that I would need to tell PKHeX that there was an active postcard effect, and if there's a way to do that, I don't know it.