A notice of non payment indicates that there is a potential lienor has an unpaid balance and helps to preserve the right to enforce a lien against the property of the potential lienor is not paid.
If you receive a Notice of Non Payment, you should not ignore it because to do so may request in you paying twice for the same work.
If you receive a Notice of Non Payment you should consider consulting an attorney.
If you are on a bonded job and it is less than 90 days since you last day on the job. This time frame is the same as the claim of lien.