[Ethereum] How should I multiply ether by a decimal

You can create some getters to return the string representations of your enum.

Example:

contract MyContract {
  enum MyEnum { Foo, Bar }

  event ThingHappened(string _e);

  function getMyEnumKeys() public constant returns (string, string) {
    return ("Foo", "Bar");
  }

  function getMyEnumKeyByValue (MyEnum myEnum) public constant returns (string) {
    if (MyEnum.Foo == myEnum) return "Foo";
    if (MyEnum.Bar == myEnum) return "Bar";
    return "";
  }

  function getMyEnumValueByKey (string myEnum) external constant returns (MyEnum) {
    if (sha3(myEnum) == sha3("Foo")) return MyEnum.Foo;
    if (sha3(myEnum) == sha3("Bar")) return MyEnum.Bar;
    revert();
  }

  function foo(string _e) {
    MyEnum myEnum = getMyEnumValueByKey(_e);
    // do something with myEnum
    ThingHappened(_e);
  }
}

However, I think the best solution would be to just have it in your public documentation that Foo is 0 and Bar is 1.

receive() has priority over fallback(). You have both of them in your contract so the receive will be called and not the fallback.

And there is no reason for it to fail if it does nothing and its payable so my guess is maybe you complied the code in remix but you forgot to deploy it again and you called the attack on an old implementation.