We have built an invocable action that could be used with code to create and delete Eventbrite promo codes. Using flows you can create a new action, look for Create a Discount Code.
When you have the action fill out the details as follows:
Discount Code - The name of the promo code example promo 1
Event Id - The Eventbrite Event Id which can be obtained via the Salesforce Eventbrite record.
Percentage Off - The discounted amount which must be expressed as a number e.g. 15% would be 15
https://jumpshare.com/embed/OiGPfBa626LL0JMFqU9O
Need a hand?