Error : “Updating failed: The response is not a valid JSON response” with custom shortcode

Problem solved, I replaced all function calls that return HTML with :

ob_start();
myFunctionDisplayHTML();  
return ob_get_clean();

And the JSON response is valid.

Thanks @phatskat, you got me on the right way 🙂
Solution find here

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)