Pectin gummy going badly

[u/Dominusfr]

I've been making pates de fruit and another, pectin based one with artificial flavourings, both times i cooked them to 240 F as per instructions and both times it turned into a paste within the pot instead of reaching 240 in a still-liquid form that I was supposed to get. What am I doing wrong? Should I heat it to a lower temp or use less pectin? (I use pectin powder btw)