Hi @NiklasBauer, 

Welcome to the Community! 

Yes, this is definitely something you can do! I would create a signup form that adds users to your main list when they sign up via form. This feature is formatted when you click the button in your form builder, make sure it submits users to the correct list you want! 
 

Someone else in the Community asked a very similar question, linked below, that I think would be helpful to check out as well. 

After your form is created, connect this list to your Welcome series Flow and have your first flow message be a ‘thanks for signing up and here’s your discount’ message. I’d check out our documentation to learn more about how to upload coupons into an email. 

For additional learning, I’d check out these helpful resources to gain more insight! 

• Getting Started with Klaviyo Academy Course
• Product Certification Academy Course

Thanks for participating in the Community!

-Taylor