Monazite calls that is interrupted in request flow

[Shorouq]

Hello,

I'm encountering an issue with Apigee where I need to monetize 400 Bad Request calls. The problem is that since the fault is occurring in the request flow, the calls are not being monetized as shown below. 

Below is the product transaction rule: 

I've explored various solutions, and I've listed all them below:

1- Use Assignee message to assignee the variable response.reason.phrase with Bad Request  in both request and response flows. 

2- Add JS policy to set a response to context.targetResponse. 

How can I configure Apigee to ensure that 400 Bad Request calls are still monetized despite faults in the request flow?

Thanks,