Export to I3S in Context Capture

Hi, I am a student and new to Context Capture. I am working on a project which requires me to produce a model in ESRI I3S format. However in the production phase I am unable to select the ESRI I3S format from the droop down list as it is greyed out.

Is there a workflow available to export to ESRI I3S format? Am I doing something wrong or have I missed a step if the option is greyed out?

I have successfully created a 3MX model from the same set of photographs, is it possible to export this 3MX model to I3S format?

Thank you.