IPSEC vpn on fortigate by using Cisco anyconnect

Hi All, 

I am using Fortigate 30E with version 5.6.7. i want to make remote ip sec vpn through cisco anyconnect software. After doing all configurations on firewall when i am going to connect with cisco any connect software it does not connect. and shows us the error on cisco anyconnect. 

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9:19:26 AM Connection attempt has failed. 9:19:26 AM No valid certificates available for authentication. 9:19:26 AM Connection attempt has failed.

Kindly help what configurations are required on forigate to connect cisco anyconnect. 

Waiting for the response.