403 Error User email is not valid

The messenger is not launching on our site and I’m getting the following error message in the console; 

1. {type: "error.list", request_id: null, errors: [{code: "403", message: "User email is not valid"}]}
   1. errors: [{code: "403", message: "User email is not valid"}]
      1. 0: {code: "403", message: "User email is not valid"}
   2. request_id: null
   3. type: "error.list"

We don’t have identity verification turned on for web, the domain is listed as trusted and the messenger is set to show on this page. 

Does anyone have any ideas on how to resolve this? I’ve raised a support ticket with Intercom but it’s been 3 days and I haven’t heard anything so any help is much appreciated! 

Thank you :)