On the manual of a Mac Mini late 2010 model, Apple recommends using a 1066MHz DDR3 SODIMM memory to upgrade the memory.

I’ve tried using a Kingston KVR KVR1333D3S9/4G but it ended up beeping whenever I tried to put the top memory stick.

I tried using Markvision BMD34096M1333C9-1121 and it worked perfectly as you can see below