Hi @Hao.Tang1,
I do not have information regarding the internal test IP, 159.220.34.142. However, I would recommend the client uses the IP 192.165.219.152 which is defined in the connection options document.
I have tried the 159.220.34.142. The IP address works with the following URL.
https://159.220.34.142/v1/Authentication/RequestToken
However, for 192.165.219.152, the IP address works with the following URL.
https://192.165.219.152/RestApi/v1/Authentication/RequestToken
Could you ask the client to add "RestApi" in the URL for 192.165.219.152/?