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';