If the connection with Xero Project or Payroll is needed to be disconnected either permanently or temporarily, following screenshots are needed to be followed:

Click on the Xero Settings tab in order to view the Xero Settings.

If you wish to end the current Xero session, simply click on  Unauthenticate Project or Unauthenticate Payroll button without selecting the checkbox.
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If you wish to delete all the Xero Projects related data (xero users, projects, tasks assocaitions, etc) stored in the SINC. Click on the checkbox for Delete Xero Payroll related data  and then click on Unathenticate Project button. 

And if you wish to delete all the Xero Payroll related data (pay schedules, employee assocaitions, etc) stored in the SINC. Click on the checkbox for  Delete Xero Payroll related data  and then click on Unauthenticate Payroll button as shown below.

Once the unauthentication (with delete Xero-related data as checked) is successful, you will be shown that your current session has been terminated and the next time you wish to authenticate, you will have to go through the Xero setup process again.

Keep in mind: You have to be careful when un-authentication process is underway because if the checkbox Delete Xero-related Project Data  or  Delete Xero-related Payroll Data is selected, it would delete all the data that is stored in SINC backend permanently. Hence, there will be no alternative way to restore the deleted information.