The PM3 is notoriously tricky to get a good coupling, especially on implants that are a little deeper.
I am assuming you have done some reserch on the forum to find placement suggestions
Here’s an example
This is a shit answer, and I have never suggested this before, but a cheap confirmation could be something like grabbing one of these
NZ$ 10.26 | RF USB RFID Card Reader For Android Mini 125khz TK4100 or 13.56mhz MF NFC Portable Scanner Type C
https://a.aliexpress.com/_mKIKw2y
I have one and it reads really easily, much easier than the PM3, it will confirm your implant is working, but thats about all.