Hi Megalight
If you don't want to show your theme on browser just delete or comment all code inside master.blade.php you will find this file " $root_folder/resources/themes/velocity/views/layouts/master.blade.php " on this path but make sure you have original copy of this file.
So by doing this api will work normally but instead of showing theme layout it will show blank page when you hit url.
You can also use java script code inside master.blade.php (after deleting or commenting default code) to redirect it to admin login if you wish.
Thanks!