Error execute Post URL

Hi Helpper. I have one problem with method PostURL of Zoho, please help me soon. This is my issue.

This is my code:

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string = "{\"listObject\":[";

for each form in forms

{

// Set make profile date == current date

form.make_date = zoho.currentdate;

// Create string to send to MyAPP

string = string + "{";

string = string + "\"fileContents\":\"" + form.file_upload + "\",";

string = (string + "\"shareBy\":\"" + zoho.adminuser) + "\",";

string = string + "\"appLinkName\":\"myapp\",";

string = string + "\"viewLinkName\":\"data_View\",";

string = string + "\"recordId\":\"" + form.ID + "\",";

string = string + "\"formname\":\"InputForm\",";

string = string + "\"fieldname\":\"file_upload\",";

string = string + "\"userLoginSkydesk\":\"" + zoho.loginuser + "\"";

string = string + "},";

}

string = string.subString(0,(string.length() - 1));

string = string + "]}";

//info string;

// Request Header

header = map();

header.put("Content-Type", "application/json");

// Send data to MyAPP

info "---------------0";

// Fetch data from url using HTTP POST request.

info "---------------1";

resp = postUrl(url, string, header, false);

info "---------------2";

....

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please show help my why resp = postUrl(url, string, header, false);

Thanks so much!