I have read about what you want to do, but what you are trying to do is impossible, In order to run Checkpoint you need to run the Rosalina-based homebrewlauncher, which can only be done when you have installed Luma3DS, it does not work with any hax-based entrypoints (for example soundhax or ninjahax)
You need to follow 3ds.hacks.guide in order to install boot9strap and Luma3DS and then once finished you can install Checkpoint as a .cia file to your home menu on your 3ds. (Or run it using the rosalina-based homebrew launcher)