Scenario: A Citrix Administrator configured the HTTP_Callout feature on the Citrix ADC using the command-line...

 The administrator should negate the expression of the Responder policy to avoid the HTTP callout recursion issue. According to the Citrix documentation, “If you configure an HTTP callout policy that is bound globally, you must ensure that the policy expression does not match the callout request. Otherwise, the callout request will trigger the policy, resulting in a callout recursion.” The expression in option B ensures that the policy does not match the callout request by adding the NOT operator at the end.

https://docs.citrix.com/en-us/citrix-adc/13/appexpert/http-callout/http-callout-policy.html