@artizenstudio, @misslaidlaw – Do either of you have a link we can look at? By default the popups are responsive if you choose any of the sizes like nano, small etc.
However the content itself is out of our control. We do our best to include some default styles that make things like images responsive inside the popups but often themes override those with their own so it could simply be a CSS issue as well.
Hard to tell without looking.
@saurabhsingh4k – Your link 404s, sorry for the delay, if you still need help let me know how I can check it out.