Save is enabled only when everything adds up:

• Days Per Week, Meals Per Day and Price all have a value;
• the delivery-day numbers add up to exactly Days Per Week;
• the category numbers are either all zero or add up to exactly Meals Per Day (the red text "Meals per day is equal to "N" and you have selected a total of "M" categories" tells you they don't);
• on a Custom plan, every category that has meals has portion counts that add up to that category's meals (the tally next to the category reads "X of N assigned" in red until it matches).

The same checks run again when you click Save; failures show inside the pop-up (for example "DaysPerWeek empty", "MealsPerDay empty", or the duplicate-combination message).