Hi friends. I was doing some problems on tsumego pro and I ran into this problem.
I solved it easily and then I wanted to try other possibilities.
I thought I found another solution but the app said it’s wrong.
Can anyone tell me why it doesn’t work? What can white do? I’m just a new player so I wouldn’t be surprised if I missed something. Thanks for your help.
This problem is a bit higher as a basic problem.
Many players, even intermediate levels, would play like you did and miss the stone sacrifice for a clean killing.
So no worries 
Edit: i wrongly deleted my first answer.
So:
In your solution there is a ko to win. Not in the “book” solution.
I was about to say the same thing as Groin.(edit, ok Groin edited by hopefully this still makes sense)
The thing about tsumego is that there is a sequence of priority of solutions. There are threads on this and I’m no expert but it’s something like:
Some problem might have “solutions” in 2 of those ways, like the one you shared but in that case the correct solution is the higher priority one.
And actually it’s probably the case that within ko there might be different sorts where one type of more favourable and is the correct solution even if other types might technically work.
“What can white do?”
White can play outside of the shown part of the board.
If you respond to White doing that, then White takes the ko back.
If you ignore White doing that, then the difference is,
how many moves elsewhere does White get before you play elsewhere?
That problem is in set of “easy problems” of Tsumego Pro. I remember when I was 10k trying for a long time to solve it, without success. I thought the problem was wrong and I was so amazed when I looked at the solution that I’ll remember it for life. It’s definitely not an “easy” problem.
