Sending a 'eth_estimateGas' always returns 53000

[erba]

Hi, I would like to do a 'estimateGas' but I want to send it as a JSON-Rpc and not use the ethers method.
But it fails unfortunately.

So, if I do it through ethers it works:

    final Web3Provider mmProv = Web3Provider(ethereum);
    final BigInt gas = await mmProv.call<BigInt>(
      'estimateGas',
      [
        TransactionRequest(
          from: accountAddress,
          to: smartContractAddress,
          data: payload,
        )
      ],
    );

But Ethers throws another error about "UNPREDICTABLE_GAS_LIMIT" so I'm trying to avoid using it with a request like this:

final gas = await ethereum!.request(
  "eth_estimateGas",
  [
        TransactionRequest(
          from: accountAddress,
          to: smartContractAddress,
          data: payload,
        ),
    "latest",
  ],
);

but it always returns 53'000 GAS which is not correct.

Doing it like this returns also the same result:

final gas2 = await ethereum!.request(
  "eth_estimateGas",
  [
    {
      "from": accountAddress,
      "to": smartContractAddress,
      "data": hexPayload,
    },
    "latest",
  ],
);

Trying the last one in pure JS works so I must be missing something on the Dart side.
Can anyone tell me what I'm doing wrong?