Weird Issue with M.2 SSD Drive

It's been well over few weeks since I am dealing with a bizarre issue with my laptop and seems like I can't find a solution to this. Already spent countless hours on the internet only to get even more frustrated. Here is what is going on.

I purchased a Dell Latitude 7390 laptop couple of months back from online. It's using an Intel 8th Gen U processor with 16GB DDR4 memory. I had Windows 10 Professional installed on it and I am quite happy with the overall performance of this small little machine that I only use when I am on the move. This laptop has a 256GB M.2 SATA SSD Drive which where I have my Windows installed. Naturally this is my primary drive and I was look for an option to have another Drive to this machine for my documents and files.

So, I have two options here. First, I can get a larger SSD Drive and make another partition on it or simply to get another physical SSD drive to the machine. After researching for few minutes, I came to realize that this machine has additional two other M.2 slot. One for WiFi and Bluetooth module and second one is for WWAN/SSD card. Naturally, I thought I can simply add another SSD drive on it to get what I was looking for.

Well, things wasn't as easy as I was thinking off. That WWAN/SSD M.2 slot must be an PCIe based Drive and it should be of 2242mm in size. So, without even digging any further, I ordered Samsung's PM991 M.2 SSD. After receiving the item, I realized I missed out and important criteria, the card must have B key cutout on it. So, this one obviously didn't work. I swapped it to the main M.2 slot and it was recognized right away and I thought of using this at some point as my primary drive.

Basically I am back to square one and I was again on the market to hunt for another M.2 PCIe based SSD drive with similar attributes. I found one soon enough and I ordered it right away with great hope and excitement. It was Toshiba KBG40ZMT128GB which has B+M key and of 2242mm size. I waited for few days and when I got the drive in my hand, I didn't wait for a minute to try it out. It was perfect but alas it was not recognized by my Laptop.

Now I am even more frustrated and desperate to find the answer of my question, why it didn't get recognized. Surprisingly, just like before I swapped this SSD on my primary drive's slot and it was recognized right away. So, what possibly could be the issue here? Is it the Drive itself or it is a fact that WWAN slot does not support SSD drive depsite the fact that the motherboard has the label on it?

I am still searching for the answer of this question and will try out few more options to get to the bottom of this issue. Now, wish me luck with that.

January 16, 2023 Update: After spending quite sometime researching on this issue, I found the answer of my question. A M.2 slot can be used with SATA, PCIe or even USB interface. Generally hardware manufacturer can decide which protocol to be used. Turns out my laptop's WWAN M.2 slot is using USB protocol thus it could not detect the PCIe SSD card.