State laws differ regarding how you can get your license back after a suspension. You will need to check with the state's Department of Motor Vehicles (DMV) in the state which you did not pay the ticket to find out what the reinstatement procedure is your driver's license after getting it suspended for your failure to comply with your traffic citation.
For example in Florida if you fail to pay a traffic ticket your driver license is suspended indefinitely. The FL Department of Highway Safety and Motor Vehicles notes that one who has not paid a Florida ticket and has had their license suspended should contact the traffic court in the county where the traffic summons was issued and satisfy the traffic summons. After this is done the motorist must then present proof of the satisfaction plus a $47.50 reinstatement fee in any Florida driver license office to get their license back.
In the State of Washington a failure to pay or respond to the ticket within 15 days results in an order that the infraction was committed. If you asked for a hearing and do not appear your payment is due immediately. When an infraction is not paid in a timely manner or a hearing missed, a $52 late penalty is added to the amount shown on the ticket. Your license may then be suspended if the penalty is not paid following a notice to pay the increased penalty, and the account may be assigned to a collection agency. So here you must pay the larger fine amount and get your license reinstated, which may also come with a reinstatement fee.
To find out what the fine or penalty will be for the seat belt ticket and what additional late fees or reinstatement fees will be due check with the court listed on the ticket and also the DMV if your notice does not give you the information you need to reinstate your driver's license.