How can I transfer playlists and favorites from one account to another on same platform ?

Even if it's not possible to connect multiple accounts of the same service in same time on Soundiiz, there's a workaround to transfer your datas between them. 

Using Soundiiz as destination

1. Connect your first account to Soundiiz
2. Transfer all your datas to "Soundiiz" as destination
3. Disconnect your first account and connect the second account
4. Transfer all your datas from "Soundiiz" to this new account as destination

Using CSV Files

1. Connect your first account to Soundiiz
2. Export all your datas as CSV file
3. Disconnect your first account and connect the second account
4. Import all your CSV to this new account

You will be able to copy your playlists but also your favorites tracks, artists and albums (if supported) between two accounts on same service.