Keep trying, but with the same sweet spot as the xNT. There’s an issue with a few Android phones where they have trouble reading ISO 15693 tags like the Spark 1. On some phones it’s intermittent, others it doesn’t work at all. Restart the device and see if you can get it to read after a few tries. Use the TagInfo app by NXP if you’re encountering issues. Let us know how it goes.