Fix Paddle Checkout Error -- 2

I'm integrating Paddle into the backend of my digital-goods store on Replit and keep running into a blocking message: “It says it's a checkout erro.” Everything else is wired up, but the checkout refuses to complete and I can’t see what I’m missing.

What I need from you
• jump into my Replit project (I’ll share the workspace)
• trace the Paddle backend flow—webhooks, server-side validation, any environment variables that matter—and pinpoint why the checkout fails
• apply the fix, then run a live or sandbox transaction to prove it works
• walk me through the change so I can maintain it on my own

The codebase is small and the problem feels configuration-related, so an experienced Paddle integrator should sort it quickly. If additional keys, webhook endpoints, or signature checks are wrong, please adjust as needed and document the tweaks before handing back.