Upon clicking 'View in Xero' you'll be able to see the invoice record that was created on Xero.
If you need to void an invoice you can do that in Accelerate or Xero and the other will be kept in sync.
If you void the invoice in Accelerate it is immediately updated on Xero and if you void it within Xero then it will be automatically updated to Void in Accelerate within a few minutes.