Have you entered your ads account to see "Account Spending Limit Reached” under the Delivery column here? :
An account spending limit is an overall limit on how much your ad account can spend across all the ad campaigns you're running. If you set an account spending limit, delivery of your ads will stop when that limit is reached to help ensure that you don't pay more for ads than you want to. This limit is optional but we encourage users not to set this up because you will not receive a notification when the limit has been hit 🙅🏽♀️.
How can I change/reset/remove my ad account spending limit?
Only ad account admins can create, change, reset or remove an account spending limit. To change, reset or remove your ad account spending limit head into the payment settings in your ads account. You should see something like this:
Any changes you make to your limit (including creating and removing one) will take about 15 minutes to take effect. If you get an error telling you that you've made too many changes to your account spending limit, wait about an hour and try again. Currently, Facebook only allows you to change your account spending limit 10 times an hour.