There are 2 reasons why you may not have access to your message Inbox:
For Android users
If you are on Android, you may have accidentally activated the "Beta" program. The Beta program allows Everfit's internal team to test upcoming features, but the Inbox will be deactivated.
You can check by going to the app store and finding the Everfit app. If you are on the "Beta" program, it will say so. All you need to do is leave the beta program and you will be prompted to download the normal app again.
For all users
Another reason could be that your coach has the Inbox turned off, if that is not a service they provide. In that case, you can connect with your coach through email or other means of communication.