0x API not using slippage for orders that only provide a buyAmount

Question

Does the 0x API correctly determine a sellAmount when given a buyAmount and a specific slippage?

In the documentation is says the following about the slippage parameter

(Optional) The maximum acceptable slippage of the buyToken amount if sellAmount is provided; The maximum acceptable slippage of the sellAmount amount if buyAmount is provided. E.g 0.03 for 3% slippage allowed.

But both of these /swap/v1/quote requests produce the same takerAmount even with very different slippage.

slippage set to 0.1

{
  "buyToken": "0xfa5047c9c78b8877af97bdcb85db743fd7313d4a",
  "sellToken": "0x7ff4169a6b5122b664c51c95727d87750ec07c84",
  "slippagePercentage": 0.1,
  "skipValidation": "true",
  "intentOnFilling": "true",
  "buyAmount": 1000000000000000000000
}

slippage set to 0.5

{
  "buyToken": "0xfa5047c9c78b8877af97bdcb85db743fd7313d4a",
  "sellToken": "0x7ff4169a6b5122b664c51c95727d87750ec07c84",
  "slippagePercentage": 0.5,
  "skipValidation": "true",
  "intentOnFilling": "true",
  "buyAmount": 1000000000000000000000
}

API response

{
  "makerToken": "0xfa5047c9c78b8877af97bdcb85db743fd7313d4a",
  "takerToken": "0x7ff4169a6b5122b664c51c95727d87750ec07c84",
  "makerAmount": "1000000000000000000000",
  "takerAmount": "41002212925764457213198",
  "fillData": {
    "tokenAddressPath": [
      "0x7ff4169a6b5122b664c51c95727d87750ec07c84",
      "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2",
      "0xfa5047c9c78b8877af97bdcb85db743fd7313d4a"
    ],
    "router": "0xf164fc0ec4e93095b804a4795bbe1e041497b92a"
  },
  "source": "Uniswap_V2",
  "sourcePathId": "0x1cf4a7984db8f5cc1ec4dccfeae82934796000f1cc836d50a0bdbd86ec264f5e",
  "type": 0
}

Answer 1

The orders field in the response is mostly informational. They're not even fillable anywhere. The data field should have the actual sell amount adjusted for slippage (takerAmount) encoded as part of the calldata.