In-app messages are not sending when email is used in "To" field

Hello EvieMarie,

Happy to help on this!  If your SDKs are identifying people via their id identifier attribute, then the in-app messages would need to be sent with that particular identifier.  

I would recommend confirming this with your mobile developers to see if that might be the case.

We’ve outlined that here in our help documentation: https://customer.io/docs/send-in-app-message/#target-audience:

When you set up a message, the To field is the identifier
—email or ID—that your app uses to identify people in Customer.io. When a person in your campaign or broadcast is identified by the value in the To field, they’ll receive your message. If your app doesn’t identify people using the value you select, we won’t deliver your message to the person. Your messages will appear as Sent, but never Opened or Clicked. 

I hope this helps!
- Jon