No function module has been generated yet

It is possible to get the SAP ABAP warning "No function module has been generated yet" when you try to get the function module name of the Smartform although the SAP Smartform is active on a SAP system.

I have recently developed a SAP Smartform document and transport it to production system.
I first opened the SAP Smartform invoice form in Display mode with SAP transaction code "smartforms".
I tried to get the Smartforms function module name using top menu : Environment > Function module name

But I got the following warning :

No function module has been generated yet
Message no. SMARTFORMS211

In order to create the function module and use it for Smartforms debugging, ABAP developers can execute a test run of the SAP Smartform.
When SAP Smartform is open, press F8. This will generate function module and SE37 transaction code screen Function builder will be displayed with new function module name as input argument.