You somehow managed to leave the feature field of your lookup empty:
If you change this field’s content to
kern, everything should be working as expected.
Explanation: Lookups are controlled with features associated to them. Some of those features are activated by default in most programs and contexts (e.g.,
kern is activated by default for horizontal text, but not activated for vertical text), others have to be activated by the user (e.g., stylistic sets). Therefore, you want to associate almost every lookup with a feature, otherwise you will not see any effect. (The only exception are lookups that are activated by other lookups.)