Let me say I'm also not a Mac user so I will have to be a little general in the discussion.
The standard setup describes a solution that only uses one Dropbox account, not two like you have.
But I have worked with another user that has two accounts and it can work, but it seems that you have to approach it differently and I'm not sure if all options are available. We were able to get it working when using Dropbox folder i.e. the Dropbox application had to be installed.
The key thing was on the computer of the user has the Dropbox folder shared with it was necessary to use the option of Shared Folder and then to navigate to where the .moneydance sync folder is within your Dropbox folder. I believe that folders that start with a period (.) are hidden on MacOS you will need to determine how you can display such folders in finder, I can't help with that one. Once you can select the .moneydancesync folder the software should display what sync sets are available.
Ethan on 10 Feb, 2020 03:53 AM
The above comment is basically correct if you are syncing between different Dropbox accounts. You will need to use the Dropbox Folder syncing option, and the share the .moneydancesync folder that will be created between the two Dropbox accounts. This will indeed by a hidden folder on most operating systems. The simplest way to access this hidden folder would be to set up syncing via this method on one computer, and then log into that computer's Dropbox account via a web browser at dropbox.com, The interface on the website should display all folders, even if they are hidden. You can then select this folder, and choose to share it with the other Dropbox account. Once it has synced with the other computer, you can then follow the rest of the instructions to open up a new synced file from Dropbox.