OpenVPN for android client

I got the "OpenVPN for android" client to connect to my ASG v9.

However if I select the options:
"Except TLS Server" : Check whether the server uses a TLS server certificate 

The connection fail to establish with:

SSL3_GET_SERVER_CERTIFICATE: certificate verify failed
TLS object-> incoming plaintext read error

Is this normal? Is it ok to leave it disable?

Thanks!

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