Error
Xero Validation Error: TaxType '<Tax Code>' was not found for the organisation.
Applies to: ConnectWise, Xero
How can this happen?
A Tax Code in Xero that has been assigned to an account has been archived/deleted.
When this Tax Code is archived, the tax rate for that Account is still pointing to the archived Tax Code.
Solution
Identify the affected Xero account, using the GL Account Mapping of the Item in ConnectWise.
In Xero, locate the account code in the Chart of Accounts, select the account and update the assigned Tax Code.
Re-sync invoice.