values smaller than 0.001 sat/B can't be represented by CFeeRate, but they are not rejected.

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.0009

error code: -6
error message:
Fee rate (0.000 sat/vB) is lower than the minimum fee rate setting (1.000 sat/vB)
```

```
./src/bitcoin-cli -named sendtoaddress address=bcrt1qwkmhqum095zau5rf2velq55cq938vrd7uw8m4r amount=1.23 fee_rate=0.000000000009

error code: -3
error message:
Invalid amount

{
    return RPCHelpMan{"addmultisigaddress",
                "\nAdd an nrequired-to-sign multisignature address to the wallet. Requires a new wallet backup.\n"
                "Each key is a Bitcoin address or hex-encoded public key.\n"
                "This functionality is only intended for use with non-watchonly addresses.\n"
                "See `importaddress` for watchonly p2sh address support.\n"
                "If 'label' is specified, assign address to that label.\n",
                {
                    {"nrequired", RPCArg::Type::NUM, RPCArg::Optional::NO, "The number of required signatures out of the n keys or addresses."},
                    {"keys", RPCArg::Type::ARR, RPCArg::Optional::NO, "The bitcoin addresses or hex-encoded public keys",
                        {
                            {"key", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "bitcoin address or hex-encoded public key"},
                        },
                        },
                    {"label", RPCArg::Type::STR, RPCArg::Optional::OMITTED_NAMED_ARG, "A label to assign the addresses to."},
                    {"address_type", RPCArg::Type::STR, RPCArg::DefaultHint{"set by -addresstype"}, "The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},
                },
                RPCResult{
                    RPCResult::Type::OBJ, "", "",
                    {
                        {RPCResult::Type::STR, "address", "The value of the new multisig address"},
                        {RPCResult::Type::STR_HEX, "redeemScript", "The string value of the hex-encoded redemption script"},
                        {RPCResult::Type::STR, "descriptor", "The descriptor for this multisig"},
                    }
                },
                RPCExamples{
            "\nAdd a multisig address from 2 addresses\n"
            + HelpExampleCli("addmultisigaddress", "2 \"[\\\"" + EXAMPLE_ADDRESS[0] + "\\\",\\\"" + EXAMPLE_ADDRESS[1] + "\\\"]\"") +
            "\nAs a JSON-RPC call\n"
            + HelpExampleRpc("addmultisigaddress", "2, \"[\\\"" + EXAMPLE_ADDRESS[0] + "\\\",\\\"" + EXAMPLE_ADDRESS[1] + "\\\"]\"")