In a saucepan, combine the diced mangoes, granulated sugar, and white vinegar. Place it over medium heat and stir until the sugar has dissolved.
Add the minced garlic, crushed chilli flakes, and salt to the mango mixture. Stir well to incorporate.
Allow the mixture to gently simmer. Reduce the heat to low and let it simmer for about 20-25 minutes, or until the mangoes have softened, and the sauce has thickened. Stir occasionally to prevent sticking.
Remove the saucepan from the heat and let the mixture cool slightly.
Using a blender or immersion blender, blend the mixture until it becomes smooth. Be cautious when blending hot liquids.
Once blended, return the sauce to the saucepan and place it over low heat. Simmer for an additional 5 minutes to ensure it’s thoroughly combined and heated through.
Take the sweet mango chilli sauce off the heat and let it cool to room temperature.
Transfer the sauce into sterilised jars or bottles. Seal them securely.