When utilizing the Sales objective, “Maximize value of conversions,” and Highest Value bid type, you can set a ROAS Goal. Meta will then attempt to spend your budget with a focus on maintaining your desired ROAS.
This isn’t a hard cap and there’s no guarantee that you will be able to maintain that Goal ROAS. If Meta struggles to meet your goal, you will likely have difficulty spending your budget. Because of this, set a realistic ROAS Goal.