Hi @roro_coeur,
You cannot use option variables inside your delivery as the MTA does not get the options from your marketing instance, and also does not support the GetOption() method.
You will need to read the option variable in a js activitiy prior to the delivery, or in the initialisation script of your delivery activity as something like this:
var.thisOption = getOption("readMyValue"); //readMyValue is an example option variable name
Then use it in your delivery activity as you want it: <%= vars.thisOption %>
Thanks,
Ishan