Testnet wallet rpc "not enough money" despite balance being adequate

Question

When I call get_balance:

$ curl http://127.0.0.1:2024/json_rpc -d '{"jsonrpc":"2.0","id":"0","method":"get_balance","params":{"account_index":2}}' -H 'Content-Type: application/json'
{
  "id": "0",
  "jsonrpc": "2.0",
  "result": {
    "balance": 1000000000000000,
    "blocks_to_unlock": 0,
    "multisig_import_needed": false,
    "per_subaddress": [{
      "account_index": 2,
      "address": "BhJQTaLZFYSCpjMdbDS5BjZwKw4BuvP6826VucYUdiV2NdJWc4qVwftgxRQBMzbxxHY8a4B5ahzFdQWijQTzDujA6Tbh8kB",
      "address_index": 0,
      "balance": 1000000000000000,
      "blocks_to_unlock": 0,
      "label": "Default Label",
      "num_unspent_outputs": 103,
      "time_to_unlock": 0,
      "unlocked_balance": 1000000000000000
    }],
    "time_to_unlock": 0,
    "unlocked_balance": 1000000000000000
  }

But when I call transfer_split:

$  curl"http://127.0.0.1:2024/json_rpc" -d '{"jsonrpc":"2.0","method":"transfer_split","params":{"destinations":[{"amount":999960233000000,"address":"BfmApzUD1erda9SDSjpbULMbTyRUhSpJBMjef5m185NV2EneYinTYfa2HJNwNLj6ePJFZmA3QH9hcG6i7onuu5q7Bycm5cf"}],"mixin":15,"get_tx_key":true,"account_index":2,"subaddr_indices":"","payment_id":"","priority":1,"unlock_time":0,"do_not_relay":false}}'
{
  "error": {
    "code": -17,
    "message": "not enough money"
  },
  "id": 0,
  "jsonrpc": "2.0"
}

As is obvious, 1000000000000000 > 999960233000000 so, what do I do to ammend this? Is there some fee I have to take into account?