Put the mandarin juice in a large saucepan and add the rum. Stir in sugar and bring the fruit juice to the boil, then let it simmer for another 3 - 4 minutes.
Now pour everything into prepared jars, close with a lid and turn upside down for 10 minutes. Then turn it over and let it cool down.
Another tip from me: I freeze the finished jam jars afterwards. In this way, the jam retains its beautiful color and tastes freshly cooked even after six months.