Vertical Elastic Query is not identifying Object
It looks permissions/authentication related to me.
Assuming that the 2 databases are on the same logical server, then your checklist of things to validate:
There is a login in the master database named 
There is a user in the &quot;carDB&quot; database named  mapped to the login
The SalesLT.Addresstest table exists in carDB
The user  in carDB has SELECT permissions on the SalesLT.Addresstest table
Test the above by connecting to carDB as the user and selecting from SalesLT.addresstest
There is a MASTER KEY created in the database that you are querying from
There is a CREDENTIAL in the database that you are querying from whose identity matches
the LOGIN that was created - same name and password.
The EXTERNAL DATA SOURCE is created in the database you are querying from
The EXTERNAL TABLE is created in the database you are querying from and matches the schema of SalesLT.Addresstest