You must renew your license every year. This license is available on the Exact Customer Portal and can be found at this link. You can update your Exact Synergy license by following the menu path [Modules > System > Configuration > License > Update].
Do you have an Exact Globe integration? If so, don’t forget to update the license for your integration solution as well. If you use ELIS (Exact Lightweight Integration Server), you must update this license in a timely manner. In this document You can find more information about updating this license here.