force Seq of elements to be printed on multiline in json using custom format spray json

Question

case class Apartment(towerNumber: Int, apartmentNumber: Int)

case class Township(name: String, apartments: Seq[Apartment])

When printing township pretty json, How to display all apartments by single tower number in multiple lines

have used ApartmentCustomJsonFormat for Apartment and private

case class TownshipGroupedByTowers(name: String, apartments : Seq[Seq[Apartment]])

for grouping of appartments by tower number.

my attempt is here : https://scastie.scala-lang.org/moglideveloper/prWPlLkERhSapxTIZYTlow/15

actual output :-

{
  "apartments": [["1-1", "1-2", "1-3"], ["2-1"], ["3-1", "3-2"]],
  "name": "Orion"
}

expected output (apartments that belongs to single tower should be displayed in one line) :-

{
  "apartments": [
      ["1-1", "1-2", "1-3"],
      ["2-1"],
      ["3-1", "3-2"]
    ],
  "name": "Orion"
}