Greetings,
Welcome to the forum.
I am not a HP employee.
Your motherboard supports the following RAM:
Dual channel (one DIMM per channel) memory architecture
Two DDR4 UDIMM (288-pin) sockets
Supports the following:
Supports 4 GB and 8 GB UDIMMs
Supports up to 4 GB on 32-bit systems
NOTE: 32-bit systems cannot address a full 4.0 GB of memory.
Supports up to 16 GB (unbuffered) on 64-bit computers
NOTE: Maximum memory shown reflects the capability of the hardware and can be limited further in the operating system.
HP Part surfer (Link) does not have memory for your PC available for purchase.
You can check Amazon for compatible memory modules. Your PC is limited to DDR4 2133 or, at best, DDR4 2400.
I suggest going to Crucial Memory (Link) for compatible memory.
You can have Crucial scan your PC or use your product number to find compatible memory.
You can mix memory modules but it is recommended to install memory modules in kits. You currently have one 8 GB PC4-17000 MB/s DDR4 2133 module.
Regards