how to get license key?

Here's a tutorial :D

How to get a Steam Key from your itch.io purchase

Step 1 - Find or re-request the Download page from your original Itch purchase email

If you haven't done so, find your original email with the purchase link.

Can't find your email?? Go to this page: https://itch.io/docs/buying/already-bought and you can request a FRESH DOWNLOAD EMAIL be sent to you!

The page should look something like:

Step 2 - Click "Get Steam Key", follow the instructions to get your key

Click the "Get Steam Key" button shown above. Follow the instructions to link your Steam account, verify your email if necessary and then copy the key to your clipboard. When in doubt, click Get Steam Key again and follow the instructions on screen.

You will use that key to put the game in your Steam library, so copy it to your clipboard.

Step 3 - Add your key to Steam 

Follow the steps on-screen. Once you get to this screen, paste in the Steam Key you got from step 2.

Once the key is activated, the game will show up in your library and start downloading.

Step 4 - Install and Play on Steam!

You can now download, install and play the game from your Steam library!

Troubleshooting: I didn't create an itch.io account when I bought the game!

Go to this page: https://itch.io/docs/buying/already-bought

Troubleshooting: When I open the link to get my Steam key itch displays a 404 error.

This will happen if you open the link in a browser that is not logged in to your itch account. Ensure you're logged in to itch and try again.