Whenever there is an error in signWithKeyInSlot, there will also be an "Illegal callback invocation from native module. This callback type only permits a single invocation from native code.", after investigation there is a missing "return" in the code.
Whenever there is an error in signWithKeyInSlot, there will also be an "Illegal callback invocation from native module. This callback type only permits a single invocation from native code.", after investigation there is a missing "return" in the code.