The same thing happened to me this week and I manged to find a solution. Hopefully you got sorted out a long time ago but this should help anybody else who needs it.
I flipped up the back the seat (the part that covers the front of the seat when it is in the down position).
Behind that is the similar cover which is secured to the back of the seat by four plastic cap covered screws.
The screw heads are six pointed star type so you'll need that particular driver bit).
Once these are removed, the back comes off and the the area where the red strap is located is revealed.
The red strap had come free of the lever which releases the catches on the seat (it's a simple pull down operation), so I just put it back in place and that was it. Put everything back and it's working fine.
Even if someone's strap is broken it wouldn't be hard to substitute a suitable replacement as there is no mechanism relating to the strap as such, just a basic pulling motion.
By the way, we first contacted our local Ford dealer, who quoted £84 just to look at it,
Hopefully this prevents anyone wasting their money for what is a simple fix.