In the case that a handheld device with a Zebra RFID sled attached via direct connection or Bluetooth is not picking up on RFID tags, check the following:
RFID Region is Set
Make sure the region is set for the RFID sled using Zebra's 123RFID mobile app that if not already installed to the device, can be installed through the Google Play Store or iOS App Store. Once installed to the device, launch Zebra 123RFID and Connect to the reader. Than navigate to the Settings option in the lower right corner and choose RFID. Click on Regulatory and make sure the correct Region is set for your area. Alternatively, you can connect the RFID Sled to your PC via USB and use Zebra's 123RFID Desktop application to set the region.
Try Scanning Tags in TracerPlus
If the region is correctly set, try downloading the project below to see if you are able to scan RFID tags with TracerPlus. Select a location, then press and hold the trigger to read tags.
Zebra TC20 / RFD2000 RFID Tag Scan Demo | Tracerplus
Note: Only one application can access the reader at a time so if you still have the 123RFID mobile app open or some other app using the reader it will not work. One way to confirm all other apps are closed is to reboot the device, then immediately open TracerPlus and try to scan.