Hi,
Charge back mechanism is that you invoice customers on the usage and access to the apps based on the monthly counters and that can be number of users as an example and charge it to the customers on the cost model you follow.
If you still have queries you can contact billing team - https://learn.microsoft.com/en-us/azure/azure-portal/supportability/how-to-create-azure-support-request#go-to-help--support-from-the-global-header
Hope this helps.
JS
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