Entering a discount code or special offer is not possible with Momoyoga in addition to your existing memberships and class passes.
You can add a specific (discount) membership or class pass to your offering. You can assign this discount card yourself to a yogi profile making sure you do not offer this online to be purchased by yogis themselves.
Another option is to manually change the price of the membership or class pass of a yogi after it has been purchased but not yet paid for. All orders and payments can be changed manually in Momoyoga. For example, the price of an order can be adjusted (later). The yogi then does not pay the original amount, but the amount corrected by the administrator.