Hi! Sorry for the confusion — after your 3 rolls, click a row on the score sheet (e.g. "B. STRAIGHT +30"), then click it again to confirm. The red button was just a status hint, which was misleading.
We've just updated the game based on your feedback: the button now works as a CONFIRM button, and there's a short first-time tutorial.
Refresh the page to get the new version. Thanks for the report!