Send document to zoom chat via java program - api

Question

I'm trying to send a file using zoom api, and I have a OAuth server-to-server authentication with /chat_message:write:admin in my app scope and I have tested simple message without problems. I already have a token, my ID and my recipient's ID.
My program runs and returns error 405 method not allowed.
I choose to send label.pdf file.
Zoom documentation page is: link to zoom api send document
private static final String API_ENDPOINT = "https://api.zoom.us/v2/chat/users/";
// Create API URL
URL url = new URL(API_ENDPOINT + userId + "/messages/files");
// Open connection and set request properties
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("POST");
conn.setRequestProperty("Authorization", "Bearer " + token);
conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=boundary");
byte[] pdfData = Files.readAllBytes(new File(filePath).toPath());
String boundary = "boundary";
String delimiter = "--" + boundary + "\r\n";
StringBuilder builder = new StringBuilder();
builder.append(delimiter);
builder.append("Content-Disposition: form-data; name=\"to_contact\"\r\n\r\n");
builder.append(toContact+"\r\n");
builder.append(delimiter);
builder.append("Content-Disposition: form-data; name=\"files\"; filename=\"label\"\r\n");
builder.append("Content-Type: application/pdf\r\n");
builder.append("\r\n");
builder.append(new String(pdfData, "ISO-8859-1"));
builder.append("\r\n");
builder.append("--" + boundary + "--");
conn.setDoOutput(true);
String multipartData = builder.toString();
System.out.println(multipartData);
conn.getOutputStream().write(multipartData.getBytes("UTF-8"));
// Send request and get response code and message
conn.connect();
int responseCode = conn.getResponseCode();
String responseMessage = conn.getResponseMessage();
// Check if response is successful
if (Arrays.asList(RESPONSE_CODE).contains(Integer.toString(responseCode))) {
System.out.println("File sent successfully!");
System.out.println("Response code: " + responseCode);
System.out.println("Response message: " + responseMessage);
} else {
System.out.println("Error sending file:");
System.out.println("Response code: " + responseCode);
System.out.println("Response message: " + responseMessage);
}
// Close connection
conn.disconnect();
Can anyone suggest me what's wrong?