Tactful way to explain to hubby....

I need advice on a tactful way to explain to my hubby that I'm not producing enough milk and need to suplement or go full formula... I've tried everything under the sun to increase my breastmilk but nothing's working. My husband keeps saying that I'm producing enough and if I'm not my body was designed for it and it will make more when needed. He just doesn't understand and won't listen to me when I try to explain. Any tactful ways that can help him understand?