Pull down firmly on the press handle to set the rivet.

Check that the rivet is firmly set:

Pull on each side of the rivet to test that it's secure.

The front and back pieces should be parallel to each other, not set at an angle.

The rivet shouldn't be able to spin.

If the rivet spins, reattach the head to the head die, line up the nail piece with the nail die, and pull again firmly on the hand press.