Download the latest master.
Use the ESP8266 libraries 2.4.2 or 2.7.2 in the board manager.
OnStep: In its Config.h change no baud rate settings but configure for your device. Then flash it.
WiFi Addon: In its Config.h change no settings at all. Then flash it into the WeMos D1 Mini. Use the "LOLIN Wemos D1 and Mini" selection. Change only the setting so it wipes all flash memory on upload.
Connect everything together.
Report on the WeMos D1 Mini blue led. Does it flash and eventually turn solid blue?