Every time a CDR file is processed, for each customer with matching calls a new charge will be applied, titled "Call charges", with an artifact in the format of a CSV file, listing all of the customer's calls for that charge.
It is therefore recommended that you process your CDR files once during your customer's normal billing period (i.e. weekly / monthly). This will mean that in their invoice, they will only get one invoice item for call charges.
In the scenario where your customers are supplied by different telecoms providers, you will want to gather all your different provider CDRs in one processing run. To do this, simply upload your first CDR file as normal, then once in the details screen, click on "Add CDR file" at the bottom left of the screen.
From here, you can add additional CDR files, which will be listed under the File(s) area of the details page. You can repeat this process as many times as you need, before processing the CDR run. Once the CDR has been processed, all calls uploaded through the CDR files will be aggregated into a single charge against the customer, with a single artifact listing a unified itemised bill.