I'm still building a website for our client.
All of a sudden, when I click the Register button and in the next screen choose 'Single' or 'Group', nothing happens anymore. No error, but no proceeding to the 1st screen of the checkout either.
Note that just before I applied your fix from this post: https://www.joomlart.com/forums/d/23304-translate-registration-cost-on-booking-form