Victor wrote:

I have a friend that is purchasing a plane and will start a business
of tow banner. He said I could fly the plane for him without been paid
, this way I can get many hours on my logbook.

Is it legal to do banner towing on a PP license without receiving
payment for it?

No.

George Patterson
Treason is ne'er successful, Sir; what then be the reason? Why, if treason
be successful, Sir, then none dare call it treason.