This Xero error typically occurs when an income account does not exist for one or more invoice line items.
To resolve: Select a default income account to use when one cannot be found on a product level. Go to Xero > Settings & Tools to select this, or make sure that you have specified a valid income account for each product in your Recurly data base. You can specify an income account under the accounting section of a product’s edit screen. Note: If you used a previous accounting integration with Recurly and you have old income account codes specified on products you will also receive this error.