You can calculate invoice manually, by filling all the corresponding fields of invoice.
You can get data for this from Code report.
Or you can calculate invoice automatically.
When performing automatic calculation you just specify the period of invoicing.
Also you can specify manually prepaid and discount.
Next system will automatically calculate services which have been provided during period and their cost, and also the total sum of invoice.
For automatic calculation the action Calculate is used which is inside Invoice edit page.
When performing automatic calculation system first fills tab Services.
First step is to calculate the cost of Telephony service.
Telephony service name should be specified in settings of Companies or Users.
For this system sums traffic for the period of invoice and adds entry connected with corresponding Service into tab Services.
System sums only traffic which corresponds to the currency of invoice.
Currency is set in account, so you need to specify one in invoice.
Next system sums Write-offs, which are present at Company or User.
All write-offs for the invoice period add added to Services tab of invoice.
After this system calculates balance for the beginning of invoice period.
Next system sums all provided services for the invoice period, applies discount, adds prepaid.
This way the total sum of invoice is generated and balance at the end of period of invoice.
Next system fills invoice with calculated values.
After this you can generate invoice file (described in Invoice generation).
Or provide payment on the invoice.
Step-by-step instruction on invoice calculation is specified in Calculate invoice.