You need a

set

. Make it look like:

mutation {
  createPlace(data: {
    title: "Haha"
    description: "Hoho"
    location: {
      create: {
        type: "Point"
        coordinates: {
          set: [4.2, 1.5]
        }
      }
    }
  }) {
    id
  }
}

You can always inspect what the prisma resolvers expect by looking at the docs in the playground, btw.