curl --request GET \
  --url https://{defaultHost}/v1/customers/filter_schema \
  --header 'Authorization: Bearer <token>'

{
  "object": "rule_schema",
  "schema_id": "customer",
  "attributes": [
    {
      "key": "live_mode",
      "metadata": false,
      "supported_values": [],
      "type": "boolean",
      "operators": [
        "is",
        "is_not"
      ]
    },
    {
      "key": "email",
      "metadata": false,
      "supported_values": [],
      "type": "string",
      "operators": [
        "is",
        "is_not",
        "contains",
        "not_contains",
        "start_with",
        "end_with"
      ]
    },
    {
      "key": "first_name",
      "metadata": false,
      "supported_values": [],
      "type": "string",
      "operators": [
        "is",
        "is_not",
        "contains",
        "not_contains",
        "start_with",
        "end_with"
      ]
    },
    {
      "key": "last_name",
      "metadata": false,
      "supported_values": [],
      "type": "string",
      "operators": [
        "is",
        "is_not",
        "contains",
        "not_contains",
        "start_with",
        "end_with"
      ]
    },
    {
      "key": "phone",
      "metadata": false,
      "supported_values": [],
      "type": "string",
      "operators": [
        "is",
        "is_not",
        "contains",
        "not_contains",
        "start_with",
        "end_with"
      ]
    },
    {
      "key": "purchases.created_at",
      "metadata": false,
      "supported_values": [],
      "type": "date",
      "operators": [
        "is",
        "is_not",
        "is_after",
        "is_before",
        "is_on_or_after",
        "is_on_or_before"
      ]
    },
    {
      "key": "purchases.product.id",
      "metadata": false,
      "supported_values": [],
      "type": "uuid",
      "operators": [
        "is",
        "is_not"
      ]
    },
    {
      "key": "purchases.product.name",
      "metadata": false,
      "supported_values": [],
      "type": "string",
      "operators": [
        "is",
        "is_not",
        "contains",
        "not_contains",
        "start_with",
        "end_with"
      ]
    },
    {
      "key": "purchases.price.id",
      "metadata": false,
      "supported_values": [],
      "type": "uuid",
      "operators": [
        "is",
        "is_not"
      ]
    },
    {
      "key": "purchases.price.name",
      "metadata": false,
      "supported_values": [],
      "type": "string",
      "operators": [
        "is",
        "is_not",
        "contains",
        "not_contains",
        "start_with",
        "end_with"
      ]
    }
  ]
}