Rights to the money
Who has the right to the money donated to and owned by the project?
In a project with no formal leadership where no one gets paid to work on it, that ends up getting some donations, there is room for friction and unhappiness when money is spent. While getting donations might be hard, spending donations can be even harder.
Communication, consistency, transparency and fairness could be guiding principles and of course money that a project has received should be spent on activities that benefit the project in one way or another.
In many projects, there will be an implied and assumed right given to the most active and maybe founding members to have more to say about these matters. Also, like in any group with humans, some will speak louder and make their opinions made clear in a stronger way.
Be open about how the money is spent and why. Involve project members in the discussion about where and how to distribute the funds.