Indeed, the billing threshold operates based on charging the ads account when it reaches the current limit. When the threshold is reached, Facebook will charge, and only upon receiving the payment can the threshold increase. However, you may need to make successful payments a few times at the current threshold before Facebook grants you an increase. Additionally, your threshold increase request needs to be reviewed and undergo the approval process. Facebook will only raise the threshold when it trusts that your account is a reliable payer. If the threshold increase process is not approved, you can try again at a later time or submit an appeal.