curl --request GET \
  --url https://api.voltview.co.uk/v1/sites/{siteId}/annualSpendAndSavings \
  --header 'Authorization: Bearer <token>'

{
  "siteId": "<string>",
  "period": "<string>",
  "spend": 123,
  "savings": 123,
  "comparisonPeriod": "<string>",
  "previousSpend": 123,
  "spendChange": 123
}