How to prevent re-syncing of invoices/bills that have been deleted in Xero

In your settings page, under Procore > Xero Syncing there is a setting to Allow re-sync of deleted Invoices or Bills:

If this is disabled, the integration will prevent the recreation of bills or invoices in Xero once it is deleted in Xero. This would only occur if Delete matching Direct Cost when deleted in Xero was not enabled in the Xero > Procore Syncing tab, as otherwise it would not resync across from Procore.