FlexiTime allows you to attribute pay costs to different Xero tracking categories as described in this article. For more dynamic tracking categories (such as shows at a theatre) you can assign jobs to your timesheet entries and send these jobs to Xero as tracking category options. If you do not have a Jobs tab available in FlexiTime then you may need to contact FlexiTime Support to get this enabled.
You then need to go to the Connect tab under Company Settings, and specify the Payroll source for your Xero Tracking category to be Jobs.
Next, enter some jobs with the Summary of the job matching the tracking category option in Xero.
Now when time is entered you can select the job to record the costs against. The payslip for the employee will be broken down into one line per job. When those pay lines are sent through on the invoice to Xero they will include the job summary as the tracking option under the tracking category specified.
Note however that timesheets for regular work are not used in pays for Salaried employees, so this job tracking will not be applied to their pays. One reason for this is that the system cannot know how to apportion time in timesheets if the hours in the timesheets differ from the regular salary hours in the pay.