How do I add more than one requirement for an advancement?

This doesn't seem to work...
{
  "display": {
    "icon": {
      "id": "minecraft:iron_chestplate"
    },
    "title": "Iron Man",
    "description": "Get a full suit of iron armor",
    "frame": "task",
    "show_toast": true,
    "announce_to_chat": true
  },
  "parent": "test:custom/ironarmor",
  "criteria": {
    "helmet": {
      "trigger": "minecraft:inventory_changed",
      "conditions": {
        "items": [
          {
            "items": [
              "minecraft:iron_helmet"
            ]
          }
        ]
      }
    },
    "chestplate": {
      "trigger": "minecraft:inventory_changed",
      "conditions": {
        "items": [
          {
            "items": [
              "minecraft:iron_chestplate"
            ]
          }
        ]
      }
    },
    "leggings": {
      "trigger": "minecraft:inventory_changed",
      "conditions": {
        "items": [
          {
            "items": [
              "minecraft:iron_leggings"
            ]
          }
        ]
      }
    },
    "boots": {
      "trigger": "minecraft:inventory_changed",
      "conditions": {
        "items": [
          {
            "items": [
              "minecraft:iron_boots"
            ]
          }
        ]
      }
    }
  },
  "requirements": [
    [
      "helmet",
      "chestplate",
      "leggings",
      "boots"
    ]
  ]
}