Add frozen cranberries directly to the slow cooker—no need to thaw them first.

Pour in the sugar, orange juice, orange zest, cinnamon stick, and water over the cranberries.

Stir to combine the ingredients, ensuring the cranberries are evenly coated.

Cover and cook on high for 3-4 hours or on low for 6-7 hours, stirring occasionally.

After 3 hours on high (or 6 hours on low), check the sauce. Use a potato masher to gently mash the cranberries, helping them burst. Leave the lid off for 30 minutes to 1 hour, allowing the sauce to thicken.

Remove the cinnamon stick and transfer the sauce to a serving dish.

Let it cool to room temperature before serving, or store it in the refrigerator until ready to serve.