Error while calling integration using smart service in Process Model.

There isn't much tom go on here other than whatever you're sending to the external system is being rejected as a "Bad Request". I would see if you can generate the request in a form that can be sent to the administrators of your external system and have them tell you what's wrong with it, unless you already have a specification to which your request should conform to, in which case you could self-diagnose the issue.

Everything is working fine at Dev and Test env. but not at Prod, I don't know why?

Hi Ravi, 

Can you please share more details about this?
Also, a suggestion would be to check your request body 

Hi Harsh,

Thank You for your response!

I want to inform you that I was not handling the null values in query parameter that's why the integration was breaking.

Now it is working fine after null handling.

Thank You.