One of the big takeaways from when we built Flattr almost a decade ago is:
It can be harder to get people to accept money than to get people to give money.
If one believe money to be important in creating eg a sustainable open source movement, then one needs to work at least as hard on getting people to accept and use money as on getting people to spend that money.
This is especially important to create a positive self-reinforcing loop where all actors can see the benefits in practice.