CSC (a.k.a. The Company Corporation or incorporate.com) serves as your company's registered agent, which your company authorized and requested in the incorporation or foreign qualification paperwork you completed on Clerky. The fee for the first year of their registered agent service was included in the third party fees collected by Clerky when you initially completed that paperwork. For subsequent years, your company pays its registered agent directly, which is why you received their invoice.
It is important to stay current with the fees for your registered agent's service so that your company remains in legal good standing and satisfies its legal obligation under state law to designate a registered agent in the company's state of incorporation and in each state where it conducts business.
In addition to serving as registered agent, many companies find it helpful to use their registered agent's supplemental compliance service, which assists companies with routine state compliance matters, such as annual report filings and franchise or business tax payments. If you used this service, the invoice may include fees for it as well.