How to DIY NFC Retro Charm Phone Plug

Making retro charms became a trend these days. The charms look nice and are really easy to make. The materials are also readily available through Taobao.
This time, I also tried to make a retro charms but it's different from others - its a NFC retro charm. I hid a NFC on-metal sticker into the charm and wrote a Youtube video link into it so my phone can play a lullaby from Youtube with a tap of the charm. It's also with a phone plug so I can plug it to my phone to bring it with me.

And the NFC on-metal stickers can be bought here.