When using the Highest Volume bid strategy, advertisers can choose to set a Cost Per Result Goal. This allows to establish how much you’re willing to pay for the optimized action. It’s not a hard cap, but a goal the algorithm will consider.
An example would be that you want to maintain a $10 Cost Per Purchase so you set a Cost Per Result Goal of $10. Meta will attempt to maintain that Cost Per Result, but it may be higher or lower. If Meta struggles to reach your goal, it may become more difficult to spend your budget. Avoid an overly aggressive Cost Per Result Goal or your ads may not get delivered.