QNetworkAccessManager, like most of Qt's I/O classes, works asynchronous, event loop based.

Usually that event loops comes from the Qt application object created in main().
If you had to add an explicit event loop you are probably missing that object or you forgot to call its exec() method or you have that code in a thread and forgot to call its exec() method, ...

And there should be no "QNetworkAccessManager::" in the SIGNAL() macro, only the name of signal and its argument types.

Cheers,
_