mobile application – User Dialogue – How to clearly indicate that the user name was not found and that it is impossible to connect to the server?

An application I am working on has an "offline mode" because it is frequently used in environments where mobile data is unavailable. When they are connected to the Internet and logging into an account, offline information from that account is stored on the device so that it can be connected in the absence of Internet access. .

The users of the application are the park guards and the inspectors. So I want to make sure that the language used is clear, as it may appear during fieldwork and that he will not be able to call anyone.

The error message aims to show:

When their username is not found on the device and can not connect to the server to search for new users.

It's currently what I've

User name not found and unable to connect to the server. Verify that the user name is correct or make sure that the server is connected to search for new user accounts.

Although I do not know if this is clear enough to be used (not to mention the long breath).