Compiling my custom keymap using QMK MSYS returns a multiple target patterns error

I am following the steps outlined here to customize my Planck OLKB rev6 keyboard. I'm using QMK MSYS to perform all the command line level stuff.

I followed all the steps and everything works fine up until I need to compile the keyboard and a custom keymap using the qmk compile command. I keep getting an error:

Makefile:507: *** multiple target patterns. Stop.

The issue is also present when I try to compile the default Planck keymap. I'm really not sure what I'm doing wrong or if there any additional setup that is required.

I tried compiling using the JSON keymap file obtained from QMK configurator directly and that works (qmk compile [-c] <configuratorExport.json>).