When sending a message containing Unicode characters via HTTP API, it is necessary to Triple URL encode the message to avoid any encoding issues.
For example:
Triple encoding '你好' gives the following value: %2525E4%2525BD%2525A0%2525E5%2525A5%2525BD
Encoding can also be done via various programming languages:
ASP.NET (C#)
Using System.Web.HttpUtility;
HttpUtility.UrlEncode(HttpUtility.UrlEncode(HttpUtility.UrlEncode("string")));
Java
import java.net.URLEncoder;
URLEncoder.encode(URLEncoder.encode(URLEncoder.encode("string", "UTF-8"), "UTF-8"), "UTF-8");
PHP
urldecode(urldecode(urldecode($text)));
Note: When scheduling message with HTTP API, the scheduledatetime must be URL encoded once.