Professional Plan Sync issue External HDD

Hi,

Just signed to the Professional plan with the expectation to backup and play with the cloud sync as promissed.

To start, how Im setup:

1) My Rekordbox library is locally stored on my M1 MBP. Only the library is local, the music files are ALL stored in an external 4TB SSD with the structure of the the folder managed via iTunes. iTunes is my central hub, I load everything there and then I drag the songs I need into RB for analysis and export to USB devices.

What I want to do:

Sync my RB library to dropbox so I can download to my phone for prep / use the phone as drive in emergencies etc.

What I did:

I turned on cloud library sync in my rb page, the dropbox account has been linked.

What is happening :

When I switch on collection autoupload, I select "copy" and the songs start to copy to my local mac drive, filling up space. I moved the dropbox location now to the external HDD and the same thing happens.

What I want to happen:

1) Upload the files to dropbox, not filling up my local drives as none of them have the capacity to support all that many tracks

2) Have them sync, backup on cloud, not affecting my local drive.

How can I achieve this? Moving everything will break iTunes.

Help is sorely needed. If I cant achieve this, the professional plan is no good to me!

Thx,

J