I can get a invoice on the Billings section, but not in Hotel & Guest House.
More than one extension that have the same location associated to them will cause this issue.
Change the location for each extension to be bale to draw the report.
Also Check that the Time on the PABX is very close or the same as the PC.
When Booking in, the date and time is specified. So if you time differs to much,
you will log someone in after they start making calls. and those calls will not
be on the bill. Also when you log the person out you can log them out before they actually stop
making calls.