What implant do you have?
I see you are doing an lf search, I assume you have an xEM, a NExT Implant or a FlexEM etc.
Coupling is critical, can you take a photo of how you are trying to read your implant?
Can you try a lf search with your LF xFD 
How long ago did you install implant?
What guide do you follow to setup your Proxmark?
Do you have a full sized test card to try it on?
From earlier in the thread, it’s an xSIID. Try hf search
You want the implant to be laying across the antenna, and you may need to press it into your hand a bit to get a read.
Yes, it is a xSIID
I tried hf as well with no luck 
pm3 --> hf search
[!] No known/supported 13.56 MHz tags found
The implant has almost 1 year.
I followed these instructions to setup the Proxmark. I was able to read a full sized test card.
I have try to put my hand on the antenna following the instructions, it still does not work.
Trying the other side
that is the LF antenna you are using, you want to use the other antenna on there, the flat black part
Yes, I tried both antennas the LF and the HF. For HF I tried top and bottom of the reader.
Can you show how it’s being held to your implant?
Also have you used the delay command?
It’s much easier to position the proxmark3 if you have a delay in place
Yes, I did use the delay as well:
pm3 --> msleep -t 3000; hf search
[!] No known/supported 13.56 MHz tags found
When a use the card test, it works fine. My implant seems unresponsive to the antenna of the Proxmark.
OK, THESE positions below are the ones you want to be trying, NONE of the others
Ideally, where you see the Antenna trace on the bottom board, you want to place that perpendicular to your implant, making a “+” with antenna and implant.
Try an hf tune , and record the higest voltage with your implant away from the antenna, then place your antenna on the implant, and move it around until you get the lowest possible Voltage ( record this voltage also). This SHOULD be your best coupling and therefore your best chance of reading / writing to your implant.
once you have the LOWEST voltage, DO NOT MOVE, send an hf search in that position and orientation, if it doesn’t work Keep pressing firmly, and move VERY small increments after each command until you get a read
let us know how this goes.
It may also hep to draw an outline around your xSIID
Since your phone makes your blinky blink? 
the hf tune should also make your LED blinky blink 
and at its brightest, is also likely where you should be able to get a read.
From reading your posts above, it sounds like there is some reconfiguring to do, but we need to get a read before we can tackle that issue
Basically it looks almost like the implant is going to be sitting near the center of the bottom PCB and that’s not where it should be. The trace of the hf antenna runs under half the bottom PCB (the half on the other side from the USB cable connector). The very end of the PCB have HF traces across it, so the very end of the proxmark should be sitting across your xSIID so half the xSIID is peaking out from under the bottom PCB of the proxmark… if that makes sense.
With your tips, I was able to make it blink. However, the hf search command still gives me the same answer: No known/supported 13.56 MHz tags found.
Can you get a read with your phone?
No, my phone cannot read it either.
Hmm… did your experiment at all with the kill code by chance?
No, I didn´t. Should I?
Anyway, since nothing can read it, I guess I cannot do anything 
Do you know places I could replace or implant another chip? I live in Stockholm, Sweden.
I tried with Chipster and they have stopped their chipping business.
Have you ensured that your PM3 and client are on the same version? If not, strange things can happen.
Run hw version and post the output.
The primary reason this is odd is that the LED is lighting. That means the chip is getting power from the antenna and the chip is performing. The only thing I can think of is that it might be getting enough power to light the LED but not activate the NFC functions of the chip. That would be a problem with coupling quality… But it would be really rare for that kind of thing to happen.
Sure
pm3 --> hw version
[ Proxmark3 RFID instrument ]
[ CLIENT ]
Iceman/master/v4.14831-963-gba1def240-dirty-unclean 2022-09-23 22:54:27 180bffbf5
compiled with............. MinGW-w64 12.2.0
platform.................. Windows (64b) / x86_64
Readline support.......... present
QT GUI support............ present
native BT support......... absent
Python script support..... present
Lua SWIG support.......... present
Python SWIG support....... present
[ PROXMARK3 ]
firmware.................. PM3 GENERIC
[ ARM ]
bootrom: Iceman/master/v4.14831-963-gba1def240-dirty-unclean 2022-09-23 22:56:05 180bffbf5
os: Iceman/master/v4.14831-963-gba1def240-dirty-unclean 2022-09-23 22:56:39 180bffbf5
compiled with GCC 10.1.0
[ FPGA ]
LF image 2s30vq100 2022-03-23 17:21:05
HF image 2s30vq100 2022-03-23 17:21:16
HF FeliCa image 2s30vq100 2022-03-23 17:21:27
HF 15 image 2s30vq100 2022-03-23 17:21:38
[ Hardware ]
--= uC: AT91SAM7S512 Rev B
--= Embedded Processor: ARM7TDMI
--= Internal SRAM size: 64K bytes
--= Architecture identifier: AT91SAM7Sxx Series
--= Embedded flash memory 512K bytes ( 59% used )
Weird indeed 
What do you suggest I shall do in this case? Would be better to get another NFC reader?
This is an xsiid right, do we know what happens with the pm3 if the “header” (can’t remember the proper name) is screwed up. I know most phones won’t read it maybe try that to recover see if it helps?