If the tool asks for an FSC script, you may be trying to flash a 2015+ device (like the Z3+ or Z4). For those models, it is recommended to use version 0.9.19.1 or newer.
Flashtool is a popular, free, and open-source tool used to flash firmware on Android devices. The software is compatible with Windows operating systems, including Windows 7, 8, and 10. The version you mentioned, Flashtool-0.9.18.6-windows, is one of the most widely used versions. Flashtool-0.9.18.6-windows