You can use this API to query the value that a counter has for an allowance, so you can see the usage data of your customers subscription. You'll need to enter the subscription ID and and the counter ID, which you'll find on the allowances page in the Billsby app.
This is useful if you want to check if your customers have any allowance left on their account before you permit a certain action.
Current usage for the period
When the counter was last updated