Your Flexible pass builder has a new section, Recurring add-ons. Give each
add-on a name, a price per billing period (with the separate 30+ price where
your venue prices by age), an optional VAT category, how many one client may
take, who can add it (every allowance, Unlimited only, a minimum number of
classes, or specific class amounts) and the short staff label that appears next
to the pass. The builder tells you straight away when a rule can never be met by
the allowances you sell, and the client preview lists which add-ons each
allowance can take. Publish as usual; existing memberships are never changed.

Clients see the add-ons in the online checkout under their class amount. An
add-on that needs more classes is shown greyed out with the reason, changing the
allowance removes an add-on that no longer fits and says why, and the review
and payment screens list each add-on on its own line so the amount charged is
the amount shown.

When a client or your staff changes a class allowance, the review now lists
which add-ons stay and which stop on the change date, and asks for a
confirmation before a change that stops an add-on is scheduled.

Your public pricing page, the pass embed and the pricing feed used by your own
website now list the add-ons a Flexible membership offers, with the allowances
they need, so visitors know about them before they choose.