As part of 404 Media's investigation, they uncovered that after submitting a payment, Spy Pet customers receive credits at a rate of $1 per 100 credits, which can then be used to look up individual users, the servers they are a part of, connected accounts, recent messages, and their activity in specific voice channels within a server.
Moreover, the team discovered that the service doesn't appear to have access to users' private messages and solely scrapes content from channels within Discord servers. Additionally, they contacted Spy Pet's creator, who described Discord as "basically the holy grail of scraping, since Discord is trying absolutely anything to combat scraping".
So, if you are a Discord user, keep in mind that nearly everything shared on the platform is likely being tracked and accessible to anyone for a price cheaper than a Big Mac.