It will probably not work correctly, your Nas 923+ needs server memory (ECC unbuffered).
You have 2 slots, 1 of which is now populated with 4GB ECC 2666 So-Dimm.
I recommend you upgrade:
Kingston 2666MT/s DDR4 ECC CL19 SODIMM 1Rx8 Micron F (1 x 16GB, 2666 MHz, DDR4-RAM, SO-DIMM)I recommend you to buy 2 pcs. so that the memory runs in dualchannel which gives you more performance than 1 bar in singlechannel.
You can offer the built-in memory for sale online.
Greetings Heiko
