How to attach a clincher connector to a FSR
Those connectors are designed to connect directly to the flexible substrate, so you need to trim off the metal contacts that have already been clinched onto the flexible resistor.

The drawing for the connector shows a section view that illustrates what happens when the connector is installed.  Note the two pairs of prongs that pierce the substrate and are clinched down make contact with the conductive areas:


One thing to note is that, as with many connectors, you can terminate them using a basic pair of pliers, but the connectors are really meant to be installed using specially-designed tools.  Pliers may work, but may not result in a reliable or repeatable crimp.  The connector datasheet shows the proper installation tools on the last page.  

Unfortunately these tools--even the manual hand tools--tend to be very expensive, but they're a worthwhile expense that you should plan for if you intend to do a lot of these terminations on a commercial basis.