curl --request GET \
  --url https://{instance}.omniapp.co/api/v1/user-attributes \
  --header 'Authorization: Bearer <token>'

{
  "records": [
    {
      "id": "",
      "name": "omni_user_id",
      "label": "Omni User ID",
      "type": "String",
      "multiple_values": false,
      "default_value": null,
      "description": null,
      "system": true
    },
    {
      "id": "",
      "name": "omni_user_email",
      "label": "Omni User Email",
      "type": "String",
      "multiple_values": false,
      "default_value": null,
      "description": null,
      "system": true
    },
    {
      "id": "",
      "name": "omni_user_name",
      "label": "Omni User Name",
      "type": "String",
      "multiple_values": false,
      "default_value": null,
      "description": null,
      "system": true
    },
    {
      "id": "",
      "name": "omni_user_timezone",
      "label": "Omni User Timezone",
      "type": "String",
      "multiple_values": false,
      "default_value": null,
      "description": null,
      "system": true
    },
    {
      "id": "",
      "name": "omni_is_org_admin",
      "label": "Omni Is Org Admin",
      "type": "String",
      "multiple_values": false,
      "default_value": null,
      "description": null,
      "system": true
    },
    {
      "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
      "name": "region",
      "label": "Region",
      "type": "String",
      "multiple_values": false,
      "default_value": "us-east",
      "description": "User region for RLS",
      "system": false
    },
    {
      "id": "b2c3d4e5-f6a7-8901-bcde-f23456789012",
      "name": "access_level",
      "label": "Access Level",
      "type": "Number",
      "multiple_values": false,
      "default_value": "1",
      "description": "Numeric access level for user permissions",
      "system": false
    },
    {
      "id": "c3d4e5f6-a7b8-9012-cdef-234567890123",
      "name": "departments",
      "label": "Departments",
      "type": "String",
      "multiple_values": true,
      "default_value": null,
      "description": "User departments for data filtering",
      "system": false
    }
  ]
}