Surely a woman must invest. When a woman has high interest or simply put high levels of respect and admiration, she will consistently invest her time, body, money and her trust in a man.
Plenty of girls offer to pay.
Even stranger's (females) at the bar at times offer to buy me a drink after some small talk. This is perfectly normal and expected when a woman finds an attractive man interesting, she wants his company.
However I've always insisted to pay. In that moment they will be under my sphere of influence. It's not about the money, it's about the frame a man projects.
The investment you guys talk about comes later and it comes from a much deeper appreciation or if you like love from women that a man has managed to generate.
Your sphere of influence generates those greater feelings in a woman.