RPC iterate nested array

[WEAUTOMATE]

Hi there!

I have a Join’s custom app.
/categories endpoint returns response like this:

[
  {
    "name": "Administration and Secretariat",
    "slug": "administration_secretariat",
    "subCategories": [
      {
        "id": 233,
        "name": "Administration and Secretariat",
        "slug": "others_administration_secretariat"
      },
      {
        "id": 229,
        "name": "Assistance, Secretarial",
        "slug": "assistance_secretarial"
      },
      {
        "id": 231,
        "name": "Clerk",
        "slug": "clerk"
      },
      {
        "id": 230,
        "name": "Office Management",
        "slug": "office_management"
      },
      {
        "id": 232,
        "name": "Property Management",
        "slug": "property_management"
      }
    ]
  },
  {
    "name": "Design and Architecture",
    "slug": "design_architecture",
    "subCategories": [
      {
        "id": 393,
        "name": "Architecture",
        "slug": "architecture"
      },
      {
        "id": 413,
        "name": "Design and Architecture",
        "slug": "others_design_architecture"
      },
      {
        "id": 395,
        "name": "Graphic Arts and Communication Design",
        "slug": "graphic_arts_communication_design"
      },
      {
        "id": 398,
        "name": "Interior Design",
        "slug": "interior_design"
      },
      {
        "id": 394,
        "name": "Media, Screen and Web Design",
        "slug": "media_screen_web_design"
      },
      {
        "id": 397,
        "name": "Photography, Video",
        "slug": "photography_video"
      },
      {
        "id": 396,
        "name": "Product Design, Industrial Design",
        "slug": "product_design_industrial_design"
      },
      {
        "id": 399,
        "name": "Wood Crafts",
        "slug": "wood_crafts"
      }
    ]
  }
]

my mappable parameters:

{
		"name": "categorySlug",
		"label": "Category",
		"required": false,
		"type": "select",
		"options": {
            "store": "rpc://categories",
            "nested": [
                {
                    "name": "subCategoryId",
                    "type": "select",
                    "label": "Sub Category",
                    "mappable": false,
                    "options": "rpc://subCategories"
                }
            ]
        }
	}

categories rpc:

{
	"url": "/categories",
	"method": "GET",
	"response": {
		"iterate": "{{body}}",
		"output": {
			"label": "{{item.name}}",
			"value": "{{item.slug}}"
		}
	}
}

sub categories rpc:

{
	"url": "/categories",
	"method": "GET",
	"response": {
		"iterate": "{{flatten(get(map(body; subCategories; slug; parameters.categorySlug); 1))}}",
		"output": {
			"label": "{{item.name}}",
			"value": "{{item.slug}}"
		}
	}
}

I need to show all sub categories as options.

Can you help me how to?