The FREEBIE discount code is applied at checkout when you're signing up for a Hey Monika Solo plan — enter it in the discount code field before completing payment, and it'll adjust the price shown before you confirm.
More detail
Enter the code in the discount field at checkout, before you confirm payment. Check the current terms, since discount codes can be time-limited or plan-specific. The discounted price will show before you complete the purchase, so you can confirm it's applied correctly.
Related reading
Hey Monika Pricing and Plans — /post/hey-monika-pricing-plans-guide
Frequently asked questions
Does FREEBIE work on both Solo and Team plans? FREEBIE is only available on the Solo plan. What if the code doesn't apply at checkout? Double-check it's been entered exactly as given (codes are case-sensitive) and that it hasn't expired — if it still doesn't apply, contact Hey Monika support.