ios openvpn authentication not work

[test00722]

it works on PC with follow command
http-proxy server 8080 "C:\\proxyauth.txt" ntlm

However, on iPhone no matter I add or delete above command in client.ovpn and input above information to "Setting">"Openvpn", enable proxy, host, port, allow basic auth, username, pw

when connecting it showed "Http proxy credentials were not accepted"

Is there anything work wrong? thanks.