I asked ChatGPT to solve the puzzle with a picture and it gave me the following:
8 1 6
3 5 7
4 9 2
That makes 15 which ever way you add the numbers, thus the game finishes and resets the grid.
Nothing more to it, no other puzzles, nothing, yet has a support button so you can email the developer if you need help, just another piece of shovel-ware.