User is getting mismatched total values when sending invoices from CORE to Xero. Some invoices can't be sent to Xero because of a tax error.
The reason for the mismatch could be that there is no service tax attached to the invoices. This amount is not sent to Xero if you have the rule Do not send MST/MET/Item Taxes as a line item to Xero checked. If you want to send the service tax amount as well, uncheck this rule.
If you are completely unable to send invoices, this error occurs when the tax codes are mismatched with the account types. The GST on Income tax code isn't supported for expense accounts in Xero. For expense accounts, make sure to use tax codes like BAS Excluded, GST on Expense, and GST free Expense.