Hello Stuart.

I am sorry to disappoint you, but unfortunately something like this is not yet possible with the plugin's built-in features, although it is planned for one of our future updates.

You can create a separate service which would offer 6 sessions for £30, and the customer would schedule the first session. Then, you can leave a custom field at the end, saying that "If you ordered a 6 session pack you will receive an e-mail with further instructions on reserving the other 5 appointments".

Then when you see this service being booked, you can create a 100% discount coupon which would expire after 5 usages, and e-mail it to the customer, so they can book the remaining 5 sessions.

Best regards.