When publishing your ads in Qwaya you'll be asked to select a bid strategy:
The options available in this section change depending on the Objective, Optimization goal and billing event that you've selected.
If you use "Lowest cost" you're telling Facebook to dynamically adjust your bid to try to get you as many results as possible while also spending your full budget evenly over the day or your ad set's lifetime (depending on the type of budget - daily or lifetime).
By setting a bid control using the bid cap bid strategy, this tells Facebook the maximum they can spend in an auction.
Bid controls are less flexible, which means they're more likely to constrain delivery than cost controls.
Bid controls limit what Facebook can bid in every auction. If you set a bid control you have more control over your cost per optimization event, but if you set one that's too low you might get less delivery.
For example, if you set a bid control of $5 and 100 optimization events become available for $5.01 bids, Facebook won't try to get any of them (they'd likely go after all of them if your cost control was $5). Facebook recommends a bid control over a cost control only if you must tightly control the cost of every optimization event you get.
Cost cap bid strategy allows you to provide Facebook with the cost of the results you care about. This enables them to deliver the maximum number of conversions as they can. The cost you provide Facebook is the average amount they try to stay under by going after the lowest cost events available.
As you spend more or increase your budget, your average cost per optimisation event might increase.
Facebook is more likely to go over your cost control during the learning phase. Bear in mind that your costs will stabilise over time and stay within the cost control after exiting the learning phase.
Minimum ROAS (return on ad spend) control helps keep your minimum ROAS per optimization event above a certain amount.
Entering a minimum ROAS control amount tells Facebook to aim to get the most purchase value and keep ROAS above the amount you enter.
Setting a minimum ROAS is a constraint on Facebook's delivery system. This means it could lead to less delivery (compared to how much you would've gotten without one) if your minimum is too high. However, if you have a specific goal for how much return you want to get from your ads, setting a minimum ROAS can help you achieve it.
If you're trying to attract new customers and can accept losing a little money in the short term because you'll make it up from the new customers over time, you could set a minimum ROAS control of 0.75. It is the equivalent of getting a 75% return on ad spend, which means if you spend $100 on your ad set, you'd want to get at least $75 of value from purchases that happen within your conversion window.
You can learn more about the differences between bid types in Facebook's help center: