Best RAM upgrade for Librem 15?

Hi, I was hoping to upgrade the RAM in a Librem 15 but I’m not terribly familiar with laptop RAM. Can someone tell me the exact requirements that need to be met and perhaps suggest a good 16 GB RAM option? I tried to look into it myself and seemed like a solid option, but it would be nice if someone could confirm for me so I don’t order something incompatible.

Also I was under the impression the supported speed was only up to 2133 MHz, but when I searched the model number of the default RAM is told me 2400 MHz. Which is the correct max speed?

Edit: No replies, tried to look up info on my own the best I could. Bought the above RAM.

I would not have bought if I were you. Never heard about this manufacturer. Better to stick to big brands (Samsung, Hynix, Corsair). I had very good experience with Crucial. However, as long as it is DDR4 at 2133 MHz - it will work.

Most probably, 2400 Mhz will work on Purism but on a lower speed.

Where did you find the model number of the installed memory?
As to Gskil, I wouldn’t be worried. They have been a common memory retailer who use good components.

I looked at the wiki, but there was no 15" one shown and a link in this forum, sent me to the V2 version. I didn’t know how many slots, or I would have maxed out my order on memory.