For those who still struggle with this problem: check if your exported JSON file has BOM marker (it depends on the server whether this marker is added to a file). When the marker is present, import doesn’t work. You can always open file in Notepad (on Windows) and save file with UTF-8 coding (not “UTF-8 with BOM”) – it should work unless your file has some syntax issues.
For those who still struggle with this problem: check if your exported JSON file has BOM marker (it depends on the server whether this marker is added to a file). When the marker is present, import doesn’t work. You can always open file in Notepad (on Windows) and save file with UTF-8 coding (not “UTF-8 with BOM”) – it should work unless your file has some syntax issues.
Some servers, while exporting JSON, add one additional byte to the file (so called BOM, https://en.wikipedia.org/wiki/Byte_order_mark). It generates errors while importing, all the JSON file should be without this additional byte. Open JSON file with Notepad, and then save it with “UTF-8” coding. Then the file should be good for importing.