The developers are aware of the issues with the new Needs Purchasing report. There’s a workaround described here:
https://discussions.scouting.org/t/how-do-we-create-advancement-report-in-scoutbook-plus/490300/8
It gets you back to the “old” Needs Purchasing report, which is still in the background for the moment (although without a convenient button to get there).
I found that I needed to log into classic Scoutbook first, then paste in the modified URL.