The issue is due to the dot (.) sign in your column name.
- To use column mapping, you should also specify structure in your source and sink dataset.
- For your source dataset, you need specify your format correctly. And since your column name has dot, you need specify the json path as following.
- You could use ADF UI to setup a copy for a single file first to get the related format, structure and column mapping format. Then change it to lookup.