For support or others to better help you can you provide further information.
What devices are you syncing between, how many computers, what are there operating systems, what version and build are running on them, e.g. 2019.4(1892).
Are you syncing to only one mobile device, your Samsung Note 9, what build of the Moneydance mobile app is it running, what Android version?
What sync method have you set up on your computers, Dropbox Folder or Dropbox Connection.
When you say “no longer works” can you give more detail.
You have only answered one of my questions that is “Syncing between desktop and this 1 phone” so I will have to assume the rest.
Your desktop is running Moneydance 2019. Your phone is running Moneydance mobile app build 1.15 for Android. You have set up the syncing method Dropbox Folder. Each of these assumptions affects the following.
I would suggest making a FILE (MONEYDANCE on Mac) - EXPORT BACKUP then proceed as follows.
On your phone under setting disconnect.
Open Moneydance and ensure on your computer “Sync Method” is set to “Don’t Sync” under FILE (MONEYDANCE on Mac) – SYNCING, then click OK.
Assuming you have Dropbox client installed using your computer in the Dropbox folder delete the folder “.moneydancesync”. Watch the Dropbox icon and wait till it states “Up to Date”. This can talk some time. Note on Mac “.moneydancesync” is hidden, try in your Finder window, typing CMD-Shift-G and then pasting ~/Dropbox/.moneydancesync/ into the box to unhide. If you don’t have Dropbox client installed you will need to sign into you Dropbox account delete “.moneydancsync” from there.
On your computer under FILE - SYNCING, set your “Encryption Passphrase”, set “Sync Method” to Dropbox Folder, click OK.
Wait for Dropbox folder “.moneydancesync” and its contents to be created. Check the Dropbox icon states “Up to Date”. This can take some time.