MassageBook Add-ons are used to enhance a Service. They can include a cost but not a duration.
When booking online, a client can only select one Service with a duration. Along with that Service, they can also choose an Add-on that doesn't include a duration. A client cannot book two Services in one appointment if they both include a duration.
If you offer an Add-on that includes a duration and want it to be available for online booking with another Service, you can build that extra time into the Service from the get-go. For example, if you offer a 60 minute Swedish massage and a 15 minute foot scrub, add a single 75 minute Service to account for both. Title, price, and describe appropriately. When booked online, the appointment will already be 75 minutes in length, and you'll know which Service and Add-on are included based on the title.
As the Business, you can book multiple Services that include a duration. When booking an appointment, select the first Service and its duration. Then, select to add another Service. You'll be able to select another Service with another duration. The appointment length will update to include both durations.
If you're using a Service as an Add-on and don't want it to be available for online booking on its own, you can hide it from your public Services page.
Additionally, you can add or extend an appointment's Recovery Time to accurately reflect the time needed.