Yes, to achieve this you have a couple of options.
Discount codes
You can use the discount code bolt-on to create a fixed amount or percentage off discount code that can only be used with the second class in a series. Participants booking their second class would then enter the code at booking. You can manually monitor that the code is being used as intended but in our experience this set up is not abused by customers.
Bundles
The second option would be to create a unique 'back-to-back' bundle that will only operate with these classes. This is a little more involved to configure but can be done within the base Gymcatch subscription.
Use 2 tags for your back-to-back classes, eg. give class 1 Tag 1 and class 2 Tag 2
Give any other none back-to-back classes on your schedule a different tag, eg. Tag 3
Create a 2 credit bundle with both Tag 1 and Tag 2 selected and only give it a short validity period, eg. 1 week.
Give your other, wider packages such as a 5 class bundle valid at all classes all 3 tags (1, 2 & 3) so they can be used with any classes.
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