Linked between jira issues

Hi Team,

For linking jira issue, i tried the below java code and below JSON. but it’s giving me below error, can any one please help on this. I do not have any access issue on jira url, i am able to update other thing using rest API by my using java code, but facing issue in linking the Jira ticket.

Used BELOW Json for LINKING -

“inward”:“is blocked by”,

Error - {“errorMessages”:[“Can not instantiate value of type [simple type, class] from JSON String; no single-String constructor/factory method”]}

Below is the my java code for linking jira issue.

CloseableHttpResponse response = null;
CloseableHttpClient httpclient = HttpClients.createDefault();
StringBuffer sb = new StringBuffer();

sb.append("{“issuelinks”:[{" add":{“type”:{“name”:“Relates”,");
sb.append("“inward”:“relates to”,");
sb.append("“outward”:“relates to”},");

	sb.append("\"outwardIssue\":  {\"key\":\"" +oldkey + "\"}}}]}");

HttpPut request = new HttpPut(jiraurl + “/rest/api/” + version
+ “/issue/”+issueid);

StringEntity params = new StringEntity(sb.toString(),"UTF-8");
	request.setHeader("X-Atlassian-Token", "nocheck");
	request.setHeader("Authorization", "Basic "
			+ jira_attachment_authentication);
	request.setHeader("content-type", "application/json");
	request.setHeader("Accept", "application/json");
	request.setHeader("Charset", "UTF-8");

	try {
		response = httpclient.execute(request);"response=" + response);
		HttpEntity entity = response.getEntity();

		if (entity != null) {

			InputStream instream = entity.getContent();
			result = HttpRequest.convertStreamToString(instream);