Hi @jayesh_joshi ,
I tried to reproduce your issue here but it works as expected. I built the test code based on phExHif demo, just put phhalHif_ConfigureWaterLevel() right before phhalHif_InitRxBuffer() as described in the API guide.

and the callback was hit right after 1 byte sent out.

You may refer to the API guide or the following for more details.

Hope that helps,
Have a great day,
Kan
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