Mix psyllium husk powder and soy milk first, and let it sit for 2-3 minutes to thicken (it will turn into a chewy jelly-like texture).
In a bowl, add protein powder, peanut butter, sweetener, salt, and any optional ingredients, then add the soaked psyllium husk mixture as well.
Mix well with a spatula or your hands, kneading until the texture is slightly sticky and tacky. (If it's too runny, add 5g more protein powder. If it's too stiff, add soy milk 1 teaspoon at a time.)
Roll the mixture into bite-sized balls.
Place the balls on a plate lined with parchment paper, then refrigerate for at least 1 hour, or freeze for 15-20 minutes to set!