Hi @Max Spilker,
Welcome to the Community! 
Before we dig deeper into this, could you please try to remove the extra fields on the Find a Profile step? Extra fields can cause issues with the Zap. You can learn more about that here: https://help.zapier.com/hc/en-us/articles/8495958376205-Why-is-there-a-section-called-Extra-Fields-on-my-Zap-action
Kindly give it a try and let me know how it goes? I'll keep an eye out for your response!
You might want to try Zenoposter. It's great for handling multi-step automations and best for email marketing like your task..
Hi Ken,
Thank you for your response. We have deleted the extra step (witch did not contain any information), but it is still not working.
@Max Spilker Hope Ken will reply 
Hi @Max Spilker,
If you're encountering an issue where a custom property key isn't recognized in your Klaviyo email, causing default text to appear instead. This may be due to a mismatch in the property key from ChatGPT, incorrect data mapping in Zapier, missing data at the time of sending, or syntax errors in your Liquid code. Ensure the property key matches precisely, the data is correctly passed and available, and the syntax follows Klaviyo's Liquid format.
I hope this helps. If you have any further questions, please don't hesitate to ask.