If the larger number is not playable at all, you are allowed to play the smaller.

You are NOT allowed to play ONLY the smaller if you could have moved the larger, or both, some other way.

This rule is NOT supported here, so we are really playing brainkinggammon, rather than backgammon. I understand that it is a bug that was prioritized low, presumably because the owner of the site is not a big proponent of the game?

For the same reason the doubling cube, which is essential to a real game, is not here either.

If backgammon is your main game go to another site.