Two major factors can impact your goal to not spend, which includes:
Product (ASIN) errors
Target ACoS is too low
To get your goal to spend more, you’d need to turn up the target ACoS on the goal. Turning up the target ACoS effectively increases the constraint on the optimization algorithm, allowing the engine to bid more on all keywords that are currently being optimized.
To learn more about why your goal is not spending, watch this Ad School video here.