Hi,

I upgraded from Paper-268 (1.16.4) to Paper-271 and Shopkeepers no longer works due to the following errors:

https://pastebin.com/zjXkzcPs

I downgraded back to Paper-268 and Shopkeepers started working again

If I'm to guess what happened. It looks like they added ignore discounts API. Which is the first thing that Shopkeepers complained on line 2. I may be mistaken.

Paper issue: PaperMC/Paper#4753