Fitted a few of these using the method recommended by the supplier B&c Express.
Having had the same trouble as you I was shocked to be told to use two hammers either side to "gently" peen over the rivets.
So, making sure the chain is dangling on to a block of wood on the floor, with lots of rag round it to ensure you don't scratch the swing arm, carefully clack away. Be careful not to put any side strain on the chain.
Check with vernier calipers and measure the peening. You only need 0.05mm or so.
Done 20K thus fitted on a couple of bikes including track days.
The Sigma R uses a hard link. Norman's method works fine. Just needs a little patience. Don't press the link on too far. Measure across the already joined links and set the same. Peen the ric=vets heads over and you're done.
Worth the trouble. They are excellent chains....................don't snap like DID