Mix the strawberry mixture with agar-agar. If desired and to taste, you can add any sweetener: fructose, stevia, honey or just sugar. Usually I add fructose (4 tsp.). A big benefit)
Put on fire and warm up until the first bubbles appear at the edges, turn down the heat and boil for 1-2 minutes, stirring occasionally. Turn off and let the marmalade cool down a little.