What would you want a finance agent to check first?

Hey all, Akash here from the Rever team. We're getting ready to launch on Product Hunt, and before that I'd love to hear from people who actually run the books.

If an agent could check one thing across every single transaction for you, what would it be? Duplicate payments, missed rebates, short payments, prices vs the contract, or something else entirely?

Real examples are welcome, especially the ones that hurt.