Sorry, this is a bug on the desktop app. It's fixed today (see our weekly update), and fix will arrive on the desktop app a few days later. Meanwhile you can still make backups on the web version, and it's not a Pro feature.
Looks like you just upgraded 19 hours ago, and Dropbox bakcups runs every 24 hours (in a few hours). Give it a few hours? It should be under Dropbox/Apps/dynalist.