I don't have any budget to buy commercial licenses but the libraries I use offer non-commercial free licenses.

How far can I go in regard to monetizing my game without it being considered commercial ? Donations? Do ads count? Optional items purchase?

For example, fmod states in their free license: 

> 
> This license cannot be used for commercial services, where the executable containing fmod is not sold, but the data is.
> 
> 
> 

What if only some data (optional) is sold?

Thank you.