You get an error message similar to this:
ERROR OCCURRED: The TaxType code TAX002 does not exist or cannot be used for this type of transaction.
WHY THIS HAPPENS:
For Xero users, tax rates must come from Xero, because Xero uses a hidden Tax Type code in its tax rate. If you get this error message, it means that the tax rate for the invoice in InvoiceASAP does not exist in Xero.
There are 3 options to fix this.
The easiest option is to edit the invoice and select a tax rate that is in your Xero.
The second option could be that your tax rate is in Xero, but the name is slightly different, so it didn't get linked to the tax rate in InvoiceASAP.
When this is the case, you will see a screen like this when you log in to the Web Dashboard.
Click on Merge Taxes, then follow the instructions to merge the InvoiceASAP tax rate with the Xero tax rate.
Create a new tax rate in Xero with EXACTLY the same name as the tax rate in InvoiceASAP.
When you run the sync, the new tax rate in Xero will link to the tax rate in InvoiceASAP, and your sync will be successful.