then change the default_envs variant in platformio.ini file
default_envs = FYSETC_S6 (For old bootloader,boot address is 0x10000, see below)
default_envs = FYSETC_S6_8000 (For new bootloader,boot address is 0x8000, see below)

Did you do this? And what did you go with? I think you should try the bottom choice first. If it wont communicate with your board then you can try the older way.

Also what Marlin did you configure? I am currently running 2.0.9.1 on some of my stuff and I think that is the latest flavor available. It might do you better to run the latest version of Marlin.