Hi I need so expert help...

I have an APEX REST POST method that is being called from an external system 'A'.

Processing this POST I need to callout to another external system 'B' and based on its response continue with my application logic, eventually returning the result to system 'A'.

The problem is that I'm getting an Error:  "System.CalloutException: Callout loop not allowed"

This is really important.

Any suggestion how can I achieve the flow I described?

Many thanks

Kruvi