Cannot apply license code

Hi, I just bought a license for my desktop app because I really like Cryptomator and want to support it, however I cannot apply it. I go to settings > support us and paste the code but there is no button to apply it. If I just close the window and restart the app, the code disappears. I have tried with the flathub version and the AppImage provided on the site. I have spent an hour now trying to apply the code. It shouldn’t be this hard.