Hi , i am also using this and it is really awesome just follow these simple steps and within few minutes you will be enjoyng your new opearting system.
Reboot your HP Envy 15-j121tx into the BIOS. Erase when the laptop boots to load the BIOS.
Now disable VT-d if enabled. That will be in CPU settings.Now Disable CFG-Lock and Secure Boot Mode.Now Enable XHCI Handoff and USB 3.0
Then Download macOS Sierra.
Run Unibeast on your pc. Click Continue Select Sierra at the Select OS Installation prompt. This will ensure the bootloader.
Select UEFI Boot Mode when you see the Bootloader Because The HP Envy 15-j121tx uses UEFI boot so we need this setting.
Follow the installation wizard to install Sierra. You should see a similar Unibeast screen to the one visible when creating the USB drive.highlight the hard drive you want to install Hackintosh.The disk will be clean Completely so make sure there is no useful data
Select OS X Extended as the format option and GUID Partition Map for the Scheme. This will format the hard drive so it will work with Sierra.
Select Install macOS and follow the installation wizard and enjoy !!!