Generally there will be a shim on the outboard pad. It's not something you add, it will be on the pad when you take it out of the box. Tin shield clipped on or a full face one that's stuck on. Some higher end pads like a Wagner thermoquiet drill right through the backer and use pad material as the shim. Missing a needed shim off the outboard pad can definitely cause a click upon initial pedal push.No shims used
Post up what the shop says.