Prerequisite: You have an FTF firmware file saved on your PC.
The flash tool is just the installer; you also need the "content" to install. You need to download the specific firmware file for the Xperia M4 Aqua. These files have the extension .ftf . sony xperia m4 aqua flash tool download
You can find it on the Sony Developer World download page . Prerequisite: You have an FTF firmware file saved on your PC
Use the built-in XperiFirm button within Flashtool to find the correct firmware for your region and model number. Quick Flashing Guide Flash tool | Developer World sony xperia m4 aqua flash tool download
Includes the XperiFirm tool to download official firmware directly from Sony servers.