Julie here from Shopify Support. Thanks for reaching out.
I haven't personally come across this error message before, so I did a quick Google search to see what I could find.
In my search, I managed this PayPal forum post, which indicates that this is a common problem for PayPal users and seems to occur across a variety of different web platforms. Based on what I'm seeing, it sounds like this error has something to do with government regulations relating to countries with trade embargoes.
Out of curiosity, is this happening with all PayPal payments from a range of different customers? Where is your business based out of? The forum post also suggests that certain business names may trigger a PayPal flag, so this may be the case as well.
It might be worth joining the conversation in that particular PayPal forum post. Since this seems to be a PayPal issue specifically, it would be best to reach out there or contact PayPal's support team for assistance. They should be able to help clear things up.
I hope this helps!