Once you change the schema in some way, you need to regenerate the code to actually see the changes in the Backend and the API.
Be careful in your choice:
Compile and Restore
Will regenerate the code, drop the current database and recreate it, trying to load your last database backup.
Use the “DB Dump” button to make a data backup before compiling if you have custom data.
Compile files
Will regenerate the code, drop the current database, recreate it with only the base data.
Compile files
Will regenerate the code. No change will be applied to the database.