It may be frustrating to see that you are getting a great ROAS in your Bottom Funnel campaign, but that you aren't spending the entire budget you set in Brainity.
This is not an error, this is occurring because of the nature of retargeting.
Retargeting ads are shown only to people who have interacted with your products. If your store is not getting a lot of traffic, this audience is going to be small.
Even though you are getting good ROAS, increasing spending is not going to continue to increase your results, because you are already effectively retargeting all your opportunities.
Forcing more budget into retargeting would require showing your small audience more ads, which can hurt performance, cause the cost per sale to increase, and annoy your potential customers.
The best way to increase your retargeting budget is to increase the number of interested people viewing your store's products.
This can be done in many ways:
Use prospecting ads to attract store visitors (With Brainity!)
Create other social media campaigns
Promote a sale
Send out a newsletter or email blast
Create a referral program
Get influencers to promote your products
Ok, but I want to spend more on Bottom of Funnel
If you want to configure your budget for each step of the funnel, you can turn on the 'Advanced Budget Configuration' if you are using the Performance plan.
Here you have a full article about how to manage your budget.