Proxy Chaining: APIProxy field

[agcifre]

Hi,

I'm chaining API proxies together . For this, I followed apigee doc https://docs.apigee.com/api-platform/fundamentals/connecting-proxies-other-proxies 

I've noticed that when I set the element 'APIProxy' with a constant value (ex: prov-dgt-dataflow-management-v1), both API Proxies are able to communicate.

However, if I set the element 'APIProxy' with the content of a variable (ex: ${my.var.api.proxy} , both proxies are not able to communicate. The messages don't even arrive to the second API Proxy.

Despite of using the same URL (or curl command).

Is it possible to use a variable to set the element 'APIProxy'? 

Is there the same limitation for the element 'Path' ?

Thanks,