Hi:
Below is the link to the service manual for your notebook.
HP Pavilion x360 m3 (model numbers m3-u100 through m3-u199, m13-u100 through m13-u199, m3-u000 throu...
According to chapter 1 of the service manual, the memory is onboard (non-removable\non-upgradable) and comes pre-configured from 4 GB up to 16 GB.
But if you look at chapter 5, there is a procedure to remove and replace the memory.
I suggest you open up the notebook and confirm that the memory can be upgraded, and then you can add an 8 GB memory chip to your notebook but it would be best to max it out to 2 x 8 GB.
When you install memory in mismatched capacities, the memory runs in the lower performing single channel mode.
When you install memory in matching capacities (2 x 4 GB, 2 x 8 GB), the memory runs in the higher performing dual channel mode.