What is the Xero integration with Vtiger CRM? What are the benefits of integrating Vtiger CRM with Xero? How do I install the Xero extension? How do I configure Xero with Vtiger? What modules in Vtiger CRM will sync with Xero? How do records sync between Vtiger CRM and Xero? In how many directions will the records sync between Vtiger and Xero? How do I set up the sync process between Xero and Vtiger CRM? How do I disable the syncing of records between Xero and Vtiger CRM? What fields are mapped for the Products and Services modules in the sync process between Vtiger and  Xero? What fields are mapped in the Invoices module for the Vtiger-Xero integration? What fields need to be mapped in the Payments module for the sync process between Vtiger and Xero? What are the conditions and limitations in the sync process between Vtiger and Xero? Can I sync a Sales account to an Invoice? What happens during syncing a sales account to an invoice? Why do I get an error about tax values when syncing invoices from Vtiger to Xero? How do I fix the issue of system accounts being used in Xero during Vtiger sync? Why am I unable to add more contacts to an organization in Xero? Is it possible to edit an invoice already approved in Xero? How do I fix the error about zero quantity in stock in Xero? How do I resolve the mismatch between the tax code and account code in Xero? Why does Xero require the Code field for a product during sync?