My wife has had trouble from time to time. Some tips-the berries should be room temperature. Mix the sugar in and give it time to liquify, a half hour or so. The pectin gets blended with the lemon juice in a separate container first, then mix it in with the fruit. Blend thoroughly, put it in your containers and leave them sit out at room temp for 24 hours.

Seems if you miss one of the steps or try to cut corners you end up with strawberry soup instead of jam. Still tastes good over ice cream.

We always make freezer jam...if you are making "regular" jam I'm uninformed.