Cannot start HCI iFlow

Hello, I am new in HCI. I have deployed simple iFlow, with soap Pole-basic authentication method, but if I run the endpoint and provide my user and password of HCI, I get following soap fault:

<faultstring>

An internal error occurred during message processing. For error details check the tail log in Integration Operations and the audit log.

</faultstring>

If I change soap authentication method to client certificate and deploy iFlow, it asks me to provide username and password if I run endpoint.

Could you please help me to start simple iFlow.