The Motion USB bridge and Homey need to be on the same local lan. If either one is on a guest network and/or there are isolation features in place on that network then Homey and the USB dongle cannot see each other. (The Motion app is a bit different because it can also function outside the lan, so that is hard to compare).
If Homey and the Motion bridge are on the same network and they cannot see each other then we need to look deeper. Try in the settings with and without entering the ip of the bridge. Restart afterward, give it a minute and then try to pair a blind. Make sure you pick the right the blind, matching what you picked in the Motion app.
You can also try to check the settings option to use separate connections for sending and receiving. That has been known to help for some.
