The first thing to do is to test with another SD card.
- If that isn't recognised either, it's a phone issue. Back to the shop to fix it under warranty. Just to be safe, check the original SD card in another device before you go.
- If another SD card is recognised, it's just a defective card. That can happen. I assume you have a backup, so don't lose anything (except some money to buy a new one).
I've had an SD card in my xcover3 for the last six months with no problems, then suddenly the phone has stopped recognising it.
Anyone got any experience of this and managed to solve it?