RFID reader can't detect blank RFID tag
You have the ground plane side of the RFID with the  metal shielded enclosure facing the tag., which is not how to couple antennae.

Then you must read the RFID manual and use it with certain modes, codes and optional encryption.


  Specs: While the DLP-RFID2 is designed to be surface mountable to the host PCB, it is not recommended that the user surface mount it to the DLP-RFID2U unless he or she intends to use only the external antennas. The ground plane on the bottom layer of the DLP-RFID2U PCB has an adverse effect on the read range of the internal antenna in the DLP-RFID2 module. If a developer wants to use the DLP-RFID2’s internal antenna while mounted to the DLP-RFID2U, then the module should be mounted using through-hole headers to raise the module up off the RFID2U PCB. The performance of the DLP-RFID2’s internal antenna will decrease as the distance between the two PCB’s decreases due to the proximity of the ground plane in the DLP-RFID2U.