Exported Tiddlers JSON error on Import

[scot]

I followed Daves tip in Documenting TW to export system tiddlers.

https://giffmex.org/gifts/documenting.tw.html#Transfer%20only%20the%20system%20tiddlers%20(or%20only%20the%20regular%20tiddlers)%20between%20files

On dragging the tiddlers.json file onto a new TW an error message is given as below.

JSON error: SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSO

Can anyone explain what has gone wrong - sorry if this question has been asked/answered before.

Scot