The mapping configuration doesn't update when you add or remove a field, or make some other change to your mapping.
Updating a Heroku Connect mapping configuration requires that the mapping is in the DATA_SYNCED state. If a poll or some other regular sync activity is happening when you edit the mapping, the changes to your mapping configuration aren't saved.
To get the mapping into the DATA_SYNCED state, you can either wait for the current sync operation to complete, or you can abort the current sync operation.
For more information, see Edit a Mapping in the Managing Heroku Connect Mappings article.