Can I re-activate a customer in Xero?

If a customer has been deactivated in Xero, is it possible to restore them inside Chargezoom?

Unfortunately, no. The way that Xero handles the de-activation and restoration process does not allow outside vendors to restore customers/clients that were previously deactivated. 

If you need to restore a client, the instructions can be found on Xero's help page here: 

https://central.xero.com/s/article/Archive-or-delete-a-client-AU#Archiveorrestoreaclient