curl --request GET \
  --url https://api.hubapi.com/marketing/v3/campaigns/{campaignGuid}/budget/totals \
  --header 'Authorization: Bearer <token>'

{
  "budgetItems": [
    {
      "amount": 123,
      "createdAt": 123,
      "id": "<string>",
      "name": "<string>",
      "order": 123,
      "updatedAt": 123,
      "description": "<string>"
    }
  ],
  "spendItems": [
    {
      "amount": 123,
      "createdAt": 123,
      "id": "<string>",
      "name": "<string>",
      "order": 123,
      "updatedAt": 123,
      "description": "<string>"
    }
  ],
  "budgetTotal": 123,
  "remainingBudget": 123,
  "spendTotal": 123
}