To create a pack or subscription that can be purchased, then used on appointment services, do the following:

Click Memberships > Subscriptions and Packs > choose which you'll create (pack or subscription) > then name it and price it.

Choose how many credits the customer will get. (Consider what you've priced your Services at when adding this figure).

Then, under 'what this can be used for', un-select any Classes that the pack/subscription should not be useable toward, then select any appointment services it should be useable toward. Save when done.

To make it make it publicly discoverable, from the memberships index page, toggle on 'featured at checkout'.

Now any customer thats self booking an appointment service included in this pack will see an option to buy this pack at checkout.