Title Column Formatting Issue

[JAPrice]

I'm working on a document library and I'm looking to basically copy the document name (from the built in doc name column) to the title column. I've come up with the formatting shown in the attached screenshot (column formatting) and this does appear to work when I paste it into the formatting field and preview it (see applying formatting 1), however as soon as I save it the formatting appears to stop working (see applying formatting 2) and then despite saying it has saved correctly when I go back in the formatting is entirely gone (see applying formatting 3). Am I doing something wrong, is the formatting code incorrect? I've done some other column formatting on this site and library without any issue so I can't work out what's going on here.

[#2 · Accepted solution]

@JAPrice I've believe managed to solve this myself now, it didn't like the title column because while it is a single line text column, the expected default value is just text and not a calculated value. After setting up and additional custom column with a calculated default value the formatting worked as expected.