Hi, Nicole. We don't have any clients who run Tixr, but we've done a lot of research on the FTC Rule. The short answer is that you need to include any mandatory fees in your "all-in" museum admission price (yes, admission is a live event). This goes for signage, online sales, receipts and any other medium in which you list your price. Any optional fees can be listed separately. If you are required to charge tax, that can be listed separately as well. We have put together an FAQ, which goes into a lot more detail.
Good luck!