Solo Tap can work with Android Phones via NFC. First, you must have both of these apps installed.
Now to use FIDO, go to a website via Chrome and either register a security key, or login and use the key to log in. For more info on how that’s typically done, see our start page. Or, you can test by going to this FIDO demo website.
The Android phone should bring up this window indicating it is time to tap you security key.
If you are having trouble getting your phone to interact with the key at this point, you may have to experiment some to find the spot on your phone where the NFC reader is. The key should be as close as possible to the back of the phone. Try pressing it against different spots on the phone each time you try to register or authenticate to find the correct NFC location.
An easy way to figure out the NFC spot, is to download the NFC TagInfo by NXP app. Open the app, and it will automatically start looking for tags. Now you can easily move your key around the back of the phone to find the NFC reader spot. The phone should vibrate as soon as it detects the security key (or other NFC device).
On the Google Pixel, you must press the token against the back of the phone in roughly this location.
On the Nexus 6, you should press the token in roughly this location.