Put the pomegranate juice in a large, nonreactive pot over medium-high heat. Meanwhile, mix the pectin and sugar in a bowl, whisking to combine. When the juice comes to a boil, add the sugar-pectin mix, whisking to stir and dissolve, and the lemon juice. Bring back to the boil and boil hard for one full minute. Turn off the heat, ladle into sterilized jars, leaving 1/8 headroom, and process via the water-bath method.