No ACK received on i2c init

Hello I am trying to integrate a I2C Slave STM32 based with PX4 over I2C.
I am using sf1xx as a template and keeping I2C address as 0x66.
While doing start I am not able to find the ack in response but same address probe and data read replicated from an I2C master over Arduino is working fine.
What can be the reason for this behaviour and how to eliminate the same.
Attached is the oscilloscope image

@DevTeam Your inputs are highly appreciated.