Is what I wish to do even possible?
Tags used for payments are high-frequency (HF) RFID tags based on the Near Field Communication (NFC) protocol. I have not seen any NFC tags in a format that can be implanted under the skin. Tags that can be implanted under the skin are low-frequency (LF) tags that come in glass ampules. Such tags do not communicate with NFC readers.
—Mark Roberti, Founder and Editor, RFID Journal