PCIe SSD card not recognized on iMac 27" Late 2013

Hello!

I have an 27" Late 2013 iMac which I just added through the PCIe connector a genuine Apple 128GB SSD card that comes from a 13" Early 2015 MacBook Air.

The whole process was a whole headache especially when I had to remove the screen, but at the end I managed to put everything in place without any issues.

I got the stock 1TB HDD and wanted to go for a PCIe SSD for better performance but now my iMac doesn't recognize the SSD card I just installed.

Disk Utility doesn't show the SSD, and the PCI section of System Report doesn't show the card.

The SSD was tested before the installation and it has no problems.

After doing some research, I noticed that the 27" iMac's from 2013/2014 only support PCIe 2.0 X2 connections while the SSD card I have installed connects to a PCIe 3.0 X4 slot.

I thought since both the PCIe slot and the SSD card are 12 + 16 pins there will be no issues.

Has anyone ever encountered this problem so far?

Thank you.