Double check if you filled in your API keys correctly. Kraken needs two API keys and in your account, you have to fill in the correct nonce.

You can read more info about the setup of your Kraken Hopper here:

Have you double-checked your API? Please refer to the following solution:

I've set everything up correctly but nothing is happening.

Maybe your start balance isn't correct. You can edit your start balance manually. Just click "edit", right next to your start balance.