But I do care. What made some projects unenjoyable was always bad process (not limited to payment processes though).
Yes, with a few months of friction and unsatisfactory conditions before. People don't complain right away esp. when there is a power imbalance. So there may be duplicate payments, delayed payments due to miscommunication and whatever little messups we had so far until something changes.
I don't see a good reason against a good default … people rarely change defaults, so that would be the process to stick to except a project manager has a reason to change it and invests the work to build and document it.
I'm not fully satisfied with any of the proposals above yet. New attempt, without requiring project managers to log into FreeAgent on Sunday, and also working for people without FreeAgent access (like one-time collaborators):
If that sounds good, I would change our documentation accordingly.