JClass Chart (which then became part of JClass DesktopViews) is/was designed for use in thick-client applications. A GUI component that’s designed for use in thick client applications isn’t meant to run in a headless mode, where there’s no UI.
Usually a headless environment is used in a server configuration (which the customer himself references, see highlight below). The current (Quest) license does not permit use of JClass Chart or other DesktopViews components in a server mode. JClass ServerChart is designed and licensed for server use, and for use in headless environments. It is API compatible with JClass Chart and it should be possible for you to use JClass ServerChart as a drop-in replacement for JClass Chart, subject to certain limitations. In particular, if you have been using JClass Chart 4.0.1K you are probably using a very old Java SDK, which may not be supported by the versions of JClass ServerViews that are currently in active support.
More detailed on headless operation are provided in the JClass ServerChart manuals.