I got the following response from api.esoui.com when I was uploading addon.
Code:
<html>
<head><title>502 Bad Gateway</title></head>
<body bgcolor="white">
<center><h1>502 Bad Gateway</h1></center>
<hr><center>cloudflare</center>
</body>
</html>
It seems api.esoui.com is not very stable.