Show users horizontal scroll is available on mobile

I am working on a project, where in the basket, just before checkout, a customer can see which seats he has selected, in which part of the room etc. Sadly, there is so much information necessary, that I can't show it on one line.

This is why I have chosen to make that specific div scrollable horizontally. One problem though: on mobiles, the div doesn't get a horizontal scroll-bar when viewed on mobiles.

I therefore need to create some kind of "call to action", so a user knows he can scroll horizontally on that specific area. What could I add design-wise, so a user knows he can interact by scrolling horizontally?

I have tried to activate a scroll bar, but it's impossible to do by code, that's why I resort to the graphic design part of SO now :)