(Progress )SyntaxError: JSON.parse: unexpected character at line 1 column 1

Hi guys,
I have previously written regarding this error that I receive :
SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
I have found the solution is just now that I have no idea how to find the file which is affected? Would anyone have any ideas, please? This error appears on debug and it causes failure when I try to upload images via chat plugin.

https://codedump.io/share/3wuOL2uCmiuM/1/how-to-solve-syntaxerror-jsonparse-unexpected-character-at-line-1-column-1-of-the-json-data-in-ajax-and-php

Thanks