Book and attend a SpendHound demo, then complete sign-up. The page ties the $500 to signing up, not to the demo by itself.
SpendHound publishes no eligibility terms for the $500. The booking form screens on ERP/accounting system and company size, and the vendor states the product is free for companies over 1,000 employees. Expect the usual screening for a prospective customer, and confirm the reward when you book.