Cascading Dropdown Menu with O365 and InfoPath 2013

Hello

I'm trying to resolve a situation where I have 2 dropdown lists in an InfoPath form on SharePoint for O365.

For example States and Cities, selecting State from DD1 displays the cities in that state in DD2. Should be fairly simple I know but unfortunately a real stumbling block for me. 

I have found a good few examples on the web but I cant get them working, I'm wondering if this a snag with the O365 version.

Many thanks

Jon