The instructions are universal; they should work for the 2.4GHz dongle, assuming it is an official "OBiWiFi" adapter, not some other brand.
I suggest restoring your OBi 200 to factory defaults, then setting it up via an Ethernet cable, confirm that works, then set up the WiFi adapter. If it doesn't work, then either it's defective, or, more likely, you are not following the instructions properly.