Get account balance

curl --request GET \
  --url https://api.case.dev/payments/v1/accounts/{id}/balance \
  --header 'Authorization: Bearer <token>'

{
  "accountId": "<string>",
  "balance": 123,
  "availableBalance": 123,
  "pendingCharges": 123,
  "heldAmount": 123,
  "currency": "<string>"
}