Why is Magento 2 showing an error for some states when I import backup rates?

When importing backup rates for the first time, you may see an error in the TaxJar extension asking you to “add a zip code”. 

The Magento extension currently supports backup rates for destination-based states and states where you have a physical nexus address. Some states have different sales tax laws for out-of-state sellers and sellers that have a physical nexus address in that state. For these states that change sourcing rules for out-of-state sellers, the extension will not import backup rates at this time.

The backup rates will not affect live sales tax calculations at checkout. These backup rates will only be used in the event that the TaxJar API is unavailable, which historically has a 99.9% uptime. Otherwise, sales tax will be calculated at checkout in realtime using the correct logic from the TaxJar API.