Hi @Jennitri O., welcome to the Community! 🎉
It looks like the Zap Search Success On Miss field is still being included. That field tells the Zap to error if a contact isn’t found, so it isn’t needed as you’re wanting to create a new contact if one isn’t found:

As the field isn’t needed but still being included I suspect that might be what’s causing the action to not work as expected.
When the Create Keap Contact if it doesn’t exist yet? option is enabled you’ll want to remove the Zap Search Success On Miss field from the Extra Fields section (appears at the bottom of the list of contact fields):

Can you try removing that field and let us know if that sorts it?
Hi @SamB Sam,
I tried removing the Zap Search Success On Miss field and still get the same error when retrying the Zap.
Sorry to hear that didn’t work as hoped, @Jennitri O. and apologies for the delay in my reply here!
I did some checking and can see that the Keap Max Classic app was made private and is no longer publicly available. I only see the Keap app available to select in my Zap:

I wonder if that might be why it’s not functioning as expected. 🤔
Can you try adding the Find or Create Contact action for the Keap app instead and see if that works correctly? If it does, then you could use that instead of the existing Keap Max Classic action in your Zap.
Hopefully that’ll do the trick, keep me posted on how it goes! 🙏