₪₪₪ If a CPA makes a mistake on your tax return, should he issue a refund?

I had a CPA prepare my tax return. We gave the information late minute but he did a good job. However, I received a letter from a state agency saying a county tax was not paid. CPA admitted he did not pay enter that tax on the state tax return . The tax owned is less than $500. Should the CPA issue a refund for this services? For how much?