Hi there @sarah.g ,

Thanks for sharing with the Community.

Can you confirm that you have properly authenticated your Facebook integration and there is no issue with the setup between your Klaviyo and Facebook account?

I would look into our two help center docs regarding Facebook:

How to Integrate with Facebook Advertising and Facebook integration data reference.

When looking at your settings, you should see that there is an option to select where you sync your list to.

If you are using a welcome flow that collects emails and sends out another to a different list, there isn't a way to automate this process to automatically add people to your main list after they have finished going through the first flow. Also, when adding them manually, there would be no way of restricting them from going through the second flow. 

In this case, the best way to combine these two lists would be to create a segment. 
The definition for this would be: 
- Is in list Facebook Lead Gen Welcome Series
OR
- Is in list 2

You will then have a flow for each list, and a segment that you can use when you want to send emails to both lists at the same time. 

Hope that helped,

Alex