I'm new in business central.
Create a table and list page. My table have 2 fields:
Code, Code 
Description, Text 
Then I create a
tableExtension and add a new field and a table relation to my table. Works fine, but when I lookup show only field code.
I need show my two field in lookup.
The problem are field Groups.
Field groups allow add field to use in your lookup.
In your table you don´t have defined the section fieldGroups.
In your case you need add this