You can use coins of any denomination, so long as they are as thick or slightly thicker than the camera bump.

Place a coin at each corner of your iPhone, and place two coins on either side of the camera bump.

Place additional coins around the entire perimeter of your iPhone.

Using a hair dryer or heat gun, evenly heat the side edges all the way around the iPhone until they are slightly too hot to touch. The heat will help the adhesive form a more complete bond. Don't overheat the iPhone, or you may cause the battery to ignite or damage other heat-sensitive components, like the display.