Hi!
That’s an interesting question but, I’m afraid, not one where we can offer too much direction. Using credits instead of conventional transactions is something that I don’t believe WooCommerce facilitates by itself – though there may be an addon that provides this sort of functionality.
The ticket products themselves are, at their heart, simply WooCommerce products – so in more general terms (such as applying promotions) you should be able to do most things that you can with WooCommerce products generally.
Does that help/clarify things?