You can easily check when your Exact Synergy license expires.
You can check the expiration date of your Exact Synergy license via the menu path [Modules > System > Setup > License > Info].
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 integration with Exact Synergy? If so, don't forget to update your Exact Synergy license 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.