Hi @MeesNijland, 

Welcome to the Community, we’re glad you’re here! I love the idea to send your new subscribers a postcard, feels very personal!

Unfortunately, it is not possible to trigger an API call in a flow. While you can use the API organized around our REST API to pull certain information about people such as a profile’s events or list and segment members, basically anything listed here can be fetched via a GET request, that would essentially export data from Klaviyo to your postcard integration. I would pay special attention to the “data warehouse” use case in the API doc to understand what the API calls are doing with the data.

Using this specific API call will allow you to send the necessary profile information to create a postcard, however, we cannot create a call in a flow to trigger that application to print the postcard. A potential workaround for this could potentially be to set up the Welcome Flow and send one of your email messages explaining that a  post-card is on the way or a “special gift” is in the mail for them.

Additionally, you could also use personalization variables in your email to still give a personalized feel.

Thanks for participating in the Community!

-Taylor