In order to trade Options on Futures, the OptionOrder.Symbol attribute must be set to the opt_underlier of the security. A list of these is attached to this post.
opt-underlier.zip
Example:
RediLib.OPTIONORDER objOrder = new RediLib.OPTIONORDER();
objOrder.Symbol = 'R.ON-.EUR';objOrder.Type = 'Call';objOrder.Date = 'May 25 '18';objOrder.Strike='2.20';