my custom screen doesn't render slots...!

[keen gulch]

I don't know what to do anymore, I've been trying for the past 2 hours to get my custom screen working. It has 9 * 4 + 5 slots (plus the inventory 9 * 4 slots)

ScreenHandler class:

class DeathboxScreenHandler : ScreenHandler {

  private val inventory: Inventory
    
  constructor(syncId: Int, playerInventory: PlayerInventory): super(ModScreenHandlers.DEATHBOX_SCREEN_HANDLER, syncId) {
    this.inventory = SimpleInventory(1)
  }
    
  constructor(syncId: Int, playerInventory: PlayerInventory, inventory: Inventory): super(ModScreenHandlers.DEATHBOX_SCREEN_HANDLER, syncId) {
    this.inventory = inventory

    for (i in 0..3) {
      for (j in 0..9) {
        this.addSlot(Slot(playerInventory, j + i * 9 + 9, 8 + j * 18, 84 + i * 18))
      }
    }

    for (i in 0..8) {
      this.addSlot(Slot(playerInventory, i, 8 + (i * 18), 142))
    }
  }

  override fun quickMove(player: PlayerEntity?, slot: Int): ItemStack {
    return ItemStack.EMPTY
  }

  override fun canUse(player: PlayerEntity?): Boolean {
    return true
  }
}

Screen class:

class DeathboxScreen(
    handler: DeathboxScreenHandler,
    inventory: PlayerInventory,
    title: Text
) : HandledScreen<DeathboxScreenHandler>(
    handler,
    inventory,
    title
) {
    private val TEXTURE = Identifier("dubacraftcoremod", "textures/gui/deathbox.png")

    init {
        this.backgroundWidth = 220
        this.backgroundHeight = 166
    }

    override fun drawBackground(ctx: DrawContext, delta: Float, mouseX: Int, mouseY: Int) {
        val x = (this.width - this.backgroundWidth) / 2
        val y = (this.height - this.backgroundHeight) / 2
        ctx.drawTexture(TEXTURE, x, y, 0, 0, this.backgroundWidth, this.backgroundHeight)
    }

    override fun render(ctx: DrawContext, mouseX: Int, mouseY: Int, delta: Float) {
        super.render(ctx, mouseX, mouseY, delta)
        this.drawMouseoverTooltip(ctx, mouseX, mouseY)
    }

    override fun drawForeground(context: DrawContext?, mouseX: Int, mouseY: Int) {

    }

}