Rinse the plums, halve, remove the pit and finely dice.
Lightly caramelize the sugar over low heat. Deglaze with the cherry juice, stirring constantly. Add 1 teaspoon of cinnamon. Simmer for about 5 minutes. Add the plums and stir in the jam sugar. Bring to a boil, stirring constantly. Add the citric acid, simmer for 1 minute and pour into jars. Seal tightly, let cool and serve.