Hi Jennifer,
I resolved the issue by deleting the ticket from the post and re-creating it
with wooCommerce set before I saved it.
When I created the ticket initially, I had RSVP selected before I saved it.
When I tried to subsequently update the ticket by selecting wooCommerce and
saving it, it would never switch to wooCommerce, however other aspects of
the ticket could be modified and saved. As I said, the solution was to just
delete the original ticket, then create it from scratch and select
wooCommerce before saving it for the first time.